Merge branch 'll_poll'

Eliezer Tamir says:

====================
This patch set adds the ability for the socket layer code to
poll directly on an Ethernet device's RX queue.
This eliminates the cost of the interrupt and context switch
and with proper tuning allows us to get very close to the HW latency.

This is a follow up to Jesse Brandeburg's Kernel Plumbers talk from
last year
http://www.linuxplumbersconf.org/2012/wp-content/uploads/2012/09/2012-lpc-Low-Latency-Sockets-slides-brandeburg.pdf

Patch 1 adds a napi_id and a hashing mechanism to lookup a napi by id.
Patch 2 adds an ndo_ll_poll method and the code that supports it.
Patch 3 adds support for busy-polling on UDP sockets.
Patch 4 adds support for TCP.
Patch 5 adds the ixgbe driver code implementing ndo_ll_poll.
Patch 6 adds additional statistics to the ixgbe driver for ndo_ll_poll.

Performance numbers:
     setup                         TCP_RR           UDP_RR
kernel  Config     C3/6 rx-usecs tps cpu% S.dem  tps cpu% S.dem
patched optimized  on   100      87k 3.13 11.4   94K 3.17 10.7
patched optimized  on   0        71k 3.12 14.0   84k 3.19 12.0
patched optimized  on   adaptive 80k 3.13 12.5   90k 3.46 12.2
patched typical    on   100      72  3.13 14.0   79k 3.17 12.8
patched typical    on   0        60k 2.13 16.5   71k 3.18 14.0
patched typical    on   adaptive 67k 3.51 16.7   75k 3.36 14.5
3.9     optimized  on   adaptive 25k 1.0  12.7   28k 0.98 11.2
3.9     typical    off  0        48k 1.09  7.3   52k 1.11 4.18
3.9     typical    0ff  adaptive 35k 1.12 4.08   38k 0.65 5.49
3.9     optimized  off  adaptive 40k 0.82 4.83   43k 0.70 5.23
3.9     optimized  off  0        57k 1.17 4.08   62k 1.04 3.95

Test setup details:
Machines: each with two Intel Xeon 2680 CPUs and X520 (82599) optical
NICs
Tests: Netperf tcp_rr and udp_rr, 1 byte (round trips per second)
Kernel: unmodified 3.9 and patched 3.9
Config: typical is derived from RH6.2, optimized is a stripped down
config.
Interrupt coalescing (ethtool rx-usecs) settings: 0=off, 1=adaptive,
100 us
When C3/6 states were turned on (via BIOS) the performance governor
was used.

These performance numbers were measured with v2 of the patch set.
Performance of the optimized config with an rx-usecs setting of 100
(the first line in the table above) was tracked during the evolution
of the patches and has never varied by more than 1%.

Design:
A global hash table that allows us to look up a struct napi by a
unique id was added.

A napi_id field was added both to struct sk_buff and struct sk.
This is used to track which NAPI we need to poll for a specific
socket.

The device driver marks every incoming skb with this id.
This is propagated to the sk when the socket is looked up in the
protocol handler.

When the socket code does not find any more data on the socket queue,
it now may call ndo_ll_poll which will crank the device's rx queue and
feed incoming packets to the stack directly from the context of the
socket.

A sysctl value (net.core4.low_latency_poll) controls how many
microseconds we busy-wait before giving up. (setting to 0 globally
disables busy-polling)

Locking:

1. Locking between napi poll and ndo_ll_poll:
Since what needs to be locked between a device's NAPI poll and
ndo_ll_poll, is highly device / configuration dependent, we do this
inside the Ethernet driver.
For example, when packets for high priority connections are sent to
separate rx queues, you might not need locking between napi poll and
ndo_ll_poll at all.

For ixgbe we only lock the RX queue.
ndo_ll_poll does not touch the interrupt state or the TX queues.
(earlier versions of this patchset did touch them,
but this design is simpler and works better.)

If a queue is actively polled by a socket (on another CPU) napi poll
will not service it, but will wait until the queue can be locked
and cleaned before doing a napi_complete().
If a socket can't lock the queue because another CPU has it,
either from napi or from another socket polling on the queue,
the socket code can busy wait on the socket's skb queue.

Ndo_ll_poll does not have preferential treatment for the data from the
calling socket vs. data from others, so if another CPU is polling,
you will see your data on this socket's queue when it arrives.

Ndo_ll_poll is called with local BHs disabled, so it won't race on
the same CPU with net_rx_action, which calls the napi poll method.

2. Napi_hash
The napi hash mechanism uses RCU.
napi_by_id() must be called under rcu_read_lock().
After a call to napi_hash_del(), caller must take care to wait an rcu
grace period before freeing the memory containing the napi struct.
(Ixgbe already had this because the queue vector structure uses rcu to
protect the statistics counters in it.)

how to test:

1. The patchset should apply cleanly to net-next.
(don't forget to configure INET_LL_RX_POLL).

2. The ethtool -c setting for rx-usecs should be on the order of 100.

3. Use ethtool -K to disable GRO and LRO
(You are encouraged to try it both ways. If you find that your
workload
does better with GRO on do tell us.)

4. Sysctl value net.core.low_latency_poll controls how long
(in us) to busy-wait for more data, You are encouraged to play
with this and see what works for you. The default is now 0 so you need
to
set it to turn the feature on. I recommend a value around 50.

4. benchmark thread and IRQ should be bound to separate cores.
Both cores should be on the same CPU NUMA node as the NIC.
When the app and the IRQ run on the same CPU  you get a small penalty.
If interrupt coalescing is set to a low value this penalty can be very
large.

5. If you suspect that your machine is not configured properly,
use numademo to make sure that the CPU to memory BW is OK.
numademo 128m memcpy local copy numbers should be more than
8GB/s on a properly configured machine.

Change log:
v10
- removed select/poll support. (we will work on this some more and try again)
v9
- correct sysctl proc_handler, reported by Eric Dumazet and Amir Vadai.
- more int -> bool changes, reported by Eric Dumazet.
- better mask testing in sock_poll(), reported by Eric Dumazet.

v8
- split out udp and select/poll into separate patches.
  what used to be patch 2/5 is now three patches.
- type corrections from Amir Vadai and Cong Wang:
  one unsigned long that was left when changing to cycles_t
  int -> bool
- more detailed patch descriptions.

v7
- suggested by Ben Hutchings and Eric Dumazet:
  type fixes, static for globals in net/core.c,
  avoid napi_id collisions in napi_hash_add()

v6
- many small fixes suggested by Eric Dumazet:
  data locality, typos, documentation
  protect napi_hash insert/delete with a spinlock (napi_gen_id is no
  longer atomic_t since it's only accessed with the spinlock held.)
- added IPv6 TCP and UDP support (only minimally tested)

v5
- corrections suggested by Ben Hutchings:
  fixed typos, moved the config option and sysctl value from IPv4 to net
- moved sk_mark_ll() to the protocol handlers
- removed global id mechanism, replaced with a hashed napi_id.
  based on code sample from Eric Dumazet
  Note that ixgbe_free_q_vector() already waits an rcu grace period
  before freeing the q_vector, so nothing additional needs to be done
  when adding a call to napi_hash_del().
- simple poll/select support

v4
- removed separate config option for TCP as suggested Eric Dumazet.
- added linux mib counter for packets received through the low latency path,
  as suggested by Andi Kleen.
- re-allow module unloading, remove module param, use a global generation id
  instead to prevent the use of a stale napi pointer, as suggested
  by Eric Dumazet
- updated Documentation/networking/ip-sysctl.txt text

v3
- coding style changes suggested by Dave Miller

v2
- the sysctl knob is now in microseconds. The default value is now 0 (off).
- for now the code depends at configure time on CONFIG_I86_TSC
- the napi reference in struct skb is now a union with the dma cookie
  since the former is only used on RX and the latter on TX,
  as suggested by Eric Dumazet.
- we do a better job at honoring non-blocking operations.
- removed busy-polling support for tcp_read_sock()
- remove dynamic disabling of GRO
- coding style fixes
- disallow unloading the device module after the feature has been used

Credit:
Jesse Brandeburg, Arun Chekhov Ilango, Julie Cummings,
Alexander Duyck, Eric Geisler, Jason Neighbors, Yadong Li,
Mike Polehn, Anil Vasudevan, Don Wood
Special thanks for finding bugs in earlier versions:
Willem de Bruijn and Andi Kleen
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/sysctl/net.txt

@@ -50,6 +50,13 @@ The maximum number of packets that kernel can handle on a NAPI interrupt,
 it's a Per-CPU variable.
 Default: 64
 
+low_latency_poll
+----------------
+Low latency busy poll timeout. (needs CONFIG_NET_LL_RX_POLL)
+Approximate time in us to spin waiting for packets on the device queue.
+Recommended value is 50. May increase power usage.
+Default: 0 (off)
+
 rmem_default
 ------------
 

drivers/net/ethernet/intel/ixgbe/ixgbe.h

@@ -52,6 +52,11 @@
 #include <linux/dca.h>
 #endif
 
+#include <net/ll_poll.h>
+
+#ifdef CONFIG_NET_LL_RX_POLL
+#define LL_EXTENDED_STATS
+#endif
 /* common prefix used by pr_<> macros */
 #undef pr_fmt
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
@@ -182,6 +187,11 @@ struct ixgbe_rx_buffer {
 struct ixgbe_queue_stats {
 	u64 packets;
 	u64 bytes;
+#ifdef LL_EXTENDED_STATS
+	u64 yields;
+	u64 misses;
+	u64 cleaned;
+#endif  /* LL_EXTENDED_STATS */
 };
 
 struct ixgbe_tx_queue_stats {
@@ -356,9 +366,133 @@ struct ixgbe_q_vector {
 	struct rcu_head rcu;	/* to avoid race with update stats on free */
 	char name[IFNAMSIZ + 9];
 
+#ifdef CONFIG_NET_LL_RX_POLL
+	unsigned int state;
+#define IXGBE_QV_STATE_IDLE        0
+#define IXGBE_QV_STATE_NAPI	   1    /* NAPI owns this QV */
+#define IXGBE_QV_STATE_POLL	   2    /* poll owns this QV */
+#define IXGBE_QV_LOCKED (IXGBE_QV_STATE_NAPI | IXGBE_QV_STATE_POLL)
+#define IXGBE_QV_STATE_NAPI_YIELD  4    /* NAPI yielded this QV */
+#define IXGBE_QV_STATE_POLL_YIELD  8    /* poll yielded this QV */
+#define IXGBE_QV_YIELD (IXGBE_QV_STATE_NAPI_YIELD | IXGBE_QV_STATE_POLL_YIELD)
+#define IXGBE_QV_USER_PEND (IXGBE_QV_STATE_POLL | IXGBE_QV_STATE_POLL_YIELD)
+	spinlock_t lock;
+#endif  /* CONFIG_NET_LL_RX_POLL */
+
 	/* for dynamic allocation of rings associated with this q_vector */
 	struct ixgbe_ring ring[0] ____cacheline_internodealigned_in_smp;
 };
+#ifdef CONFIG_NET_LL_RX_POLL
+static inline void ixgbe_qv_init_lock(struct ixgbe_q_vector *q_vector)
+{
+
+	spin_lock_init(&q_vector->lock);
+	q_vector->state = IXGBE_QV_STATE_IDLE;
+}
+
+/* called from the device poll routine to get ownership of a q_vector */
+static inline bool ixgbe_qv_lock_napi(struct ixgbe_q_vector *q_vector)
+{
+	int rc = true;
+	spin_lock(&q_vector->lock);
+	if (q_vector->state & IXGBE_QV_LOCKED) {
+		WARN_ON(q_vector->state & IXGBE_QV_STATE_NAPI);
+		q_vector->state |= IXGBE_QV_STATE_NAPI_YIELD;
+		rc = false;
+#ifdef LL_EXTENDED_STATS
+		q_vector->tx.ring->stats.yields++;
+#endif
+	} else
+		/* we don't care if someone yielded */
+		q_vector->state = IXGBE_QV_STATE_NAPI;
+	spin_unlock(&q_vector->lock);
+	return rc;
+}
+
+/* returns true is someone tried to get the qv while napi had it */
+static inline bool ixgbe_qv_unlock_napi(struct ixgbe_q_vector *q_vector)
+{
+	int rc = false;
+	spin_lock(&q_vector->lock);
+	WARN_ON(q_vector->state & (IXGBE_QV_STATE_POLL |
+			       IXGBE_QV_STATE_NAPI_YIELD));
+
+	if (q_vector->state & IXGBE_QV_STATE_POLL_YIELD)
+		rc = true;
+	q_vector->state = IXGBE_QV_STATE_IDLE;
+	spin_unlock(&q_vector->lock);
+	return rc;
+}
+
+/* called from ixgbe_low_latency_poll() */
+static inline bool ixgbe_qv_lock_poll(struct ixgbe_q_vector *q_vector)
+{
+	int rc = true;
+	spin_lock_bh(&q_vector->lock);
+	if ((q_vector->state & IXGBE_QV_LOCKED)) {
+		q_vector->state |= IXGBE_QV_STATE_POLL_YIELD;
+		rc = false;
+#ifdef LL_EXTENDED_STATS
+		q_vector->rx.ring->stats.yields++;
+#endif
+	} else
+		/* preserve yield marks */
+		q_vector->state |= IXGBE_QV_STATE_POLL;
+	spin_unlock_bh(&q_vector->lock);
+	return rc;
+}
+
+/* returns true if someone tried to get the qv while it was locked */
+static inline bool ixgbe_qv_unlock_poll(struct ixgbe_q_vector *q_vector)
+{
+	int rc = false;
+	spin_lock_bh(&q_vector->lock);
+	WARN_ON(q_vector->state & (IXGBE_QV_STATE_NAPI));
+
+	if (q_vector->state & IXGBE_QV_STATE_POLL_YIELD)
+		rc = true;
+	q_vector->state = IXGBE_QV_STATE_IDLE;
+	spin_unlock_bh(&q_vector->lock);
+	return rc;
+}
+
+/* true if a socket is polling, even if it did not get the lock */
+static inline bool ixgbe_qv_ll_polling(struct ixgbe_q_vector *q_vector)
+{
+	WARN_ON(!(q_vector->state & IXGBE_QV_LOCKED));
+	return q_vector->state & IXGBE_QV_USER_PEND;
+}
+#else /* CONFIG_NET_LL_RX_POLL */
+static inline void ixgbe_qv_init_lock(struct ixgbe_q_vector *q_vector)
+{
+}
+
+static inline bool ixgbe_qv_lock_napi(struct ixgbe_q_vector *q_vector)
+{
+	return true;
+}
+
+static inline bool ixgbe_qv_unlock_napi(struct ixgbe_q_vector *q_vector)
+{
+	return false;
+}
+
+static inline bool ixgbe_qv_lock_poll(struct ixgbe_q_vector *q_vector)
+{
+	return false;
+}
+
+static inline bool ixgbe_qv_unlock_poll(struct ixgbe_q_vector *q_vector)
+{
+	return false;
+}
+
+static inline bool ixgbe_qv_ll_polling(struct ixgbe_q_vector *q_vector)
+{
+	return false;
+}
+#endif /* CONFIG_NET_LL_RX_POLL */
+
 #ifdef CONFIG_IXGBE_HWMON
 
 #define IXGBE_HWMON_TYPE_LOC		0

drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c

@@ -1054,6 +1054,12 @@ static void ixgbe_get_ethtool_stats(struct net_device *netdev,
 			data[i] = 0;
 			data[i+1] = 0;
 			i += 2;
+#ifdef LL_EXTENDED_STATS
+			data[i] = 0;
+			data[i+1] = 0;
+			data[i+2] = 0;
+			i += 3;
+#endif
 			continue;
 		}
 
@@ -1063,6 +1069,12 @@ static void ixgbe_get_ethtool_stats(struct net_device *netdev,
 			data[i+1] = ring->stats.bytes;
 		} while (u64_stats_fetch_retry_bh(&ring->syncp, start));
 		i += 2;
+#ifdef LL_EXTENDED_STATS
+		data[i] = ring->stats.yields;
+		data[i+1] = ring->stats.misses;
+		data[i+2] = ring->stats.cleaned;
+		i += 3;
+#endif
 	}
 	for (j = 0; j < IXGBE_NUM_RX_QUEUES; j++) {
 		ring = adapter->rx_ring[j];
@@ -1070,6 +1082,12 @@ static void ixgbe_get_ethtool_stats(struct net_device *netdev,
 			data[i] = 0;
 			data[i+1] = 0;
 			i += 2;
+#ifdef LL_EXTENDED_STATS
+			data[i] = 0;
+			data[i+1] = 0;
+			data[i+2] = 0;
+			i += 3;
+#endif
 			continue;
 		}
 
@@ -1079,6 +1097,12 @@ static void ixgbe_get_ethtool_stats(struct net_device *netdev,
 			data[i+1] = ring->stats.bytes;
 		} while (u64_stats_fetch_retry_bh(&ring->syncp, start));
 		i += 2;
+#ifdef LL_EXTENDED_STATS
+		data[i] = ring->stats.yields;
+		data[i+1] = ring->stats.misses;
+		data[i+2] = ring->stats.cleaned;
+		i += 3;
+#endif
 	}
 
 	for (j = 0; j < IXGBE_MAX_PACKET_BUFFERS; j++) {
@@ -1115,12 +1139,28 @@ static void ixgbe_get_strings(struct net_device *netdev, u32 stringset,
 			p += ETH_GSTRING_LEN;
 			sprintf(p, "tx_queue_%u_bytes", i);
 			p += ETH_GSTRING_LEN;
+#ifdef LL_EXTENDED_STATS
+			sprintf(p, "tx_q_%u_napi_yield", i);
+			p += ETH_GSTRING_LEN;
+			sprintf(p, "tx_q_%u_misses", i);
+			p += ETH_GSTRING_LEN;
+			sprintf(p, "tx_q_%u_cleaned", i);
+			p += ETH_GSTRING_LEN;
+#endif /* LL_EXTENDED_STATS */
 		}
 		for (i = 0; i < IXGBE_NUM_RX_QUEUES; i++) {
 			sprintf(p, "rx_queue_%u_packets", i);
 			p += ETH_GSTRING_LEN;
 			sprintf(p, "rx_queue_%u_bytes", i);
 			p += ETH_GSTRING_LEN;
+#ifdef LL_EXTENDED_STATS
+			sprintf(p, "rx_q_%u_ll_poll_yield", i);
+			p += ETH_GSTRING_LEN;
+			sprintf(p, "rx_q_%u_misses", i);
+			p += ETH_GSTRING_LEN;
+			sprintf(p, "rx_q_%u_cleaned", i);
+			p += ETH_GSTRING_LEN;
+#endif /* LL_EXTENDED_STATS */
 		}
 		for (i = 0; i < IXGBE_MAX_PACKET_BUFFERS; i++) {
 			sprintf(p, "tx_pb_%u_pxon", i);

drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c

@@ -811,6 +811,7 @@ static int ixgbe_alloc_q_vector(struct ixgbe_adapter *adapter,
 	/* initialize NAPI */
 	netif_napi_add(adapter->netdev, &q_vector->napi,
 		       ixgbe_poll, 64);
+	napi_hash_add(&q_vector->napi);
 
 	/* tie q_vector and adapter together */
 	adapter->q_vector[v_idx] = q_vector;
@@ -931,6 +932,7 @@ static void ixgbe_free_q_vector(struct ixgbe_adapter *adapter, int v_idx)
 		adapter->rx_ring[ring->queue_index] = NULL;
 
 	adapter->q_vector[v_idx] = NULL;
+	napi_hash_del(&q_vector->napi);
 	netif_napi_del(&q_vector->napi);
 
 	/*

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -1504,7 +1504,9 @@ static void ixgbe_rx_skb(struct ixgbe_q_vector *q_vector,
 {
 	struct ixgbe_adapter *adapter = q_vector->adapter;
 
-	if (!(adapter->flags & IXGBE_FLAG_IN_NETPOLL))
+	if (ixgbe_qv_ll_polling(q_vector))
+		netif_receive_skb(skb);
+	else if (!(adapter->flags & IXGBE_FLAG_IN_NETPOLL))
 		napi_gro_receive(&q_vector->napi, skb);
 	else
 		netif_rx(skb);
@@ -1892,9 +1894,9 @@ static struct sk_buff *ixgbe_fetch_rx_buffer(struct ixgbe_ring *rx_ring,
  * expensive overhead for IOMMU access this provides a means of avoiding
  * it by maintaining the mapping of the page to the syste.
  *
- * Returns true if all work is completed without reaching budget
+ * Returns amount of work completed
  **/
-static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
+static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
 			       struct ixgbe_ring *rx_ring,
 			       const int budget)
 {
@@ -1976,6 +1978,7 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
 		}
 
 #endif /* IXGBE_FCOE */
+		skb_mark_ll(skb, &q_vector->napi);
 		ixgbe_rx_skb(q_vector, skb);
 
 		/* update budget accounting */
@@ -1992,9 +1995,43 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
 	if (cleaned_count)
 		ixgbe_alloc_rx_buffers(rx_ring, cleaned_count);
 
-	return (total_rx_packets < budget);
+	return total_rx_packets;
 }
 
+#ifdef CONFIG_NET_LL_RX_POLL
+/* must be called with local_bh_disable()d */
+static int ixgbe_low_latency_recv(struct napi_struct *napi)
+{
+	struct ixgbe_q_vector *q_vector =
+			container_of(napi, struct ixgbe_q_vector, napi);
+	struct ixgbe_adapter *adapter = q_vector->adapter;
+	struct ixgbe_ring  *ring;
+	int found = 0;
+
+	if (test_bit(__IXGBE_DOWN, &adapter->state))
+		return LL_FLUSH_FAILED;
+
+	if (!ixgbe_qv_lock_poll(q_vector))
+		return LL_FLUSH_BUSY;
+
+	ixgbe_for_each_ring(ring, q_vector->rx) {
+		found = ixgbe_clean_rx_irq(q_vector, ring, 4);
+#ifdef LL_EXTENDED_STATS
+		if (found)
+			ring->stats.cleaned += found;
+		else
+			ring->stats.misses++;
+#endif
+		if (found)
+			break;
+	}
+
+	ixgbe_qv_unlock_poll(q_vector);
+
+	return found;
+}
+#endif	/* CONFIG_NET_LL_RX_POLL */
+
 /**
  * ixgbe_configure_msix - Configure MSI-X hardware
  * @adapter: board private structure
@@ -2550,6 +2587,9 @@ int ixgbe_poll(struct napi_struct *napi, int budget)
 	ixgbe_for_each_ring(ring, q_vector->tx)
 		clean_complete &= !!ixgbe_clean_tx_irq(q_vector, ring);
 
+	if (!ixgbe_qv_lock_napi(q_vector))
+		return budget;
+
 	/* attempt to distribute budget to each queue fairly, but don't allow
 	 * the budget to go below 1 because we'll exit polling */
 	if (q_vector->rx.count > 1)
@@ -2558,9 +2598,10 @@ int ixgbe_poll(struct napi_struct *napi, int budget)
 		per_ring_budget = budget;
 
 	ixgbe_for_each_ring(ring, q_vector->rx)
-		clean_complete &= ixgbe_clean_rx_irq(q_vector, ring,
-						     per_ring_budget);
+		clean_complete &= (ixgbe_clean_rx_irq(q_vector, ring,
+				   per_ring_budget) < per_ring_budget);
 
+	ixgbe_qv_unlock_napi(q_vector);
 	/* If all work not completed, return budget and keep polling */
 	if (!clean_complete)
 		return budget;
@@ -3747,16 +3788,25 @@ static void ixgbe_napi_enable_all(struct ixgbe_adapter *adapter)
 {
 	int q_idx;
 
-	for (q_idx = 0; q_idx < adapter->num_q_vectors; q_idx++)
+	for (q_idx = 0; q_idx < adapter->num_q_vectors; q_idx++) {
+		ixgbe_qv_init_lock(adapter->q_vector[q_idx]);
 		napi_enable(&adapter->q_vector[q_idx]->napi);
+	}
 }
 
 static void ixgbe_napi_disable_all(struct ixgbe_adapter *adapter)
 {
 	int q_idx;
 
-	for (q_idx = 0; q_idx < adapter->num_q_vectors; q_idx++)
+	local_bh_disable(); /* for ixgbe_qv_lock_napi() */
+	for (q_idx = 0; q_idx < adapter->num_q_vectors; q_idx++) {
 		napi_disable(&adapter->q_vector[q_idx]->napi);
+		while (!ixgbe_qv_lock_napi(adapter->q_vector[q_idx])) {
+			pr_info("QV %d locked\n", q_idx);
+			mdelay(1);
+		}
+	}
+	local_bh_enable();
 }
 
 #ifdef CONFIG_IXGBE_DCB
@@ -7177,6 +7227,9 @@ static const struct net_device_ops ixgbe_netdev_ops = {
 #ifdef CONFIG_NET_POLL_CONTROLLER
 	.ndo_poll_controller	= ixgbe_netpoll,
 #endif
+#ifdef CONFIG_NET_LL_RX_POLL
+	.ndo_ll_poll		= ixgbe_low_latency_recv,
+#endif
 #ifdef IXGBE_FCOE
 	.ndo_fcoe_ddp_setup = ixgbe_fcoe_ddp_get,
 	.ndo_fcoe_ddp_target = ixgbe_fcoe_ddp_target,

include/linux/netdevice.h

@@ -324,12 +324,15 @@ struct napi_struct {
 	struct sk_buff		*gro_list;
 	struct sk_buff		*skb;
 	struct list_head	dev_list;
+	struct hlist_node	napi_hash_node;
+	unsigned int		napi_id;
 };
 
 enum {
 	NAPI_STATE_SCHED,	/* Poll is scheduled */
 	NAPI_STATE_DISABLE,	/* Disable pending */
 	NAPI_STATE_NPSVC,	/* Netpoll - don't dequeue from poll_list */
+	NAPI_STATE_HASHED,	/* In NAPI hash */
 };
 
 enum gro_result {
@@ -445,6 +448,32 @@ static inline bool napi_reschedule(struct napi_struct *napi)
 extern void __napi_complete(struct napi_struct *n);
 extern void napi_complete(struct napi_struct *n);
 
+/**
+ *	napi_by_id - lookup a NAPI by napi_id
+ *	@napi_id: hashed napi_id
+ *
+ * lookup @napi_id in napi_hash table
+ * must be called under rcu_read_lock()
+ */
+extern struct napi_struct *napi_by_id(unsigned int napi_id);
+
+/**
+ *	napi_hash_add - add a NAPI to global hashtable
+ *	@napi: napi context
+ *
+ * generate a new napi_id and store a @napi under it in napi_hash
+ */
+extern void napi_hash_add(struct napi_struct *napi);
+
+/**
+ *	napi_hash_del - remove a NAPI from global table
+ *	@napi: napi context
+ *
+ * Warning: caller must observe rcu grace period
+ * before freeing memory containing @napi
+ */
+extern void napi_hash_del(struct napi_struct *napi);
+
 /**
  *	napi_disable - prevent NAPI from scheduling
  *	@n: napi context
@@ -942,6 +971,9 @@ struct net_device_ops {
 						     struct netpoll_info *info,
 						     gfp_t gfp);
 	void			(*ndo_netpoll_cleanup)(struct net_device *dev);
+#endif
+#ifdef CONFIG_NET_LL_RX_POLL
+	int			(*ndo_ll_poll)(struct napi_struct *dev);
 #endif
 	int			(*ndo_set_vf_mac)(struct net_device *dev,
 						  int queue, u8 *mac);

include/linux/skbuff.h

@@ -386,6 +386,7 @@ typedef unsigned char *sk_buff_data_t;
  *	@no_fcs:  Request NIC to treat last 4 bytes as Ethernet FCS
  *	@dma_cookie: a cookie to one of several possible DMA operations
  *		done by skb DMA functions
+  *	@napi_id: id of the NAPI struct this skb came from
  *	@secmark: security marking
  *	@mark: Generic packet mark
  *	@dropcount: total number of sk_receive_queue overflows
@@ -500,8 +501,11 @@ struct sk_buff {
 	/* 7/9 bit hole (depending on ndisc_nodetype presence) */
 	kmemcheck_bitfield_end(flags2);
 
-#ifdef CONFIG_NET_DMA
-	dma_cookie_t		dma_cookie;
+#if defined CONFIG_NET_DMA || defined CONFIG_NET_LL_RX_POLL
+	union {
+		unsigned int	napi_id;
+		dma_cookie_t	dma_cookie;
+	};
 #endif
 #ifdef CONFIG_NETWORK_SECMARK
 	__u32			secmark;

include/net/ll_poll.h

+/*
+ * Low Latency Sockets
+ * Copyright(c) 2013 Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Author: Eliezer Tamir
+ *
+ * Contact Information:
+ * e1000-devel Mailing List <e1000-devel@lists.sourceforge.net>
+ */
+
+/*
+ * For now this depends on CONFIG_X86_TSC
+ */
+
+#ifndef _LINUX_NET_LL_POLL_H
+#define _LINUX_NET_LL_POLL_H
+
+#include <linux/netdevice.h>
+#include <net/ip.h>
+
+#ifdef CONFIG_NET_LL_RX_POLL
+
+struct napi_struct;
+extern unsigned long sysctl_net_ll_poll __read_mostly;
+
+/* return values from ndo_ll_poll */
+#define LL_FLUSH_FAILED		-1
+#define LL_FLUSH_BUSY		-2
+
+/* we don't mind a ~2.5% imprecision */
+#define TSC_MHZ (tsc_khz >> 10)
+
+static inline cycles_t ll_end_time(void)
+{
+	return TSC_MHZ * ACCESS_ONCE(sysctl_net_ll_poll) + get_cycles();
+}
+
+static inline bool sk_valid_ll(struct sock *sk)
+{
+	return sysctl_net_ll_poll && sk->sk_napi_id &&
+	       !need_resched() && !signal_pending(current);
+}
+
+static inline bool can_poll_ll(cycles_t end_time)
+{
+	return !time_after((unsigned long)get_cycles(),
+			    (unsigned long)end_time);
+}
+
+static inline bool sk_poll_ll(struct sock *sk, int nonblock)
+{
+	cycles_t end_time = ll_end_time();
+	const struct net_device_ops *ops;
+	struct napi_struct *napi;
+	int rc = false;
+
+	/*
+	 * rcu read lock for napi hash
+	 * bh so we don't race with net_rx_action
+	 */
+	rcu_read_lock_bh();
+
+	napi = napi_by_id(sk->sk_napi_id);
+	if (!napi)
+		goto out;
+
+	ops = napi->dev->netdev_ops;
+	if (!ops->ndo_ll_poll)
+		goto out;
+
+	do {
+
+		rc = ops->ndo_ll_poll(napi);
+
+		if (rc == LL_FLUSH_FAILED)
+			break; /* permanent failure */
+
+		if (rc > 0)
+			/* local bh are disabled so it is ok to use _BH */
+			NET_ADD_STATS_BH(sock_net(sk),
+					 LINUX_MIB_LOWLATENCYRXPACKETS, rc);
+
+	} while (skb_queue_empty(&sk->sk_receive_queue)
+			&& can_poll_ll(end_time) && !nonblock);
+
+	rc = !skb_queue_empty(&sk->sk_receive_queue);
+out:
+	rcu_read_unlock_bh();
+	return rc;
+}
+
+/* used in the NIC receive handler to mark the skb */
+static inline void skb_mark_ll(struct sk_buff *skb, struct napi_struct *napi)
+{
+	skb->napi_id = napi->napi_id;
+}
+
+/* used in the protocol hanlder to propagate the napi_id to the socket */
+static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb)
+{
+	sk->sk_napi_id = skb->napi_id;
+}
+
+#else /* CONFIG_NET_LL_RX_POLL */
+
+static inline cycles_t ll_end_time(void)
+{
+	return 0;
+}
+
+static inline bool sk_valid_ll(struct sock *sk)
+{
+	return false;
+}
+
+static inline bool sk_poll_ll(struct sock *sk, int nonblock)
+{
+	return false;
+}
+
+static inline void skb_mark_ll(struct sk_buff *skb, struct napi_struct *napi)
+{
+}
+
+static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb)
+{
+}
+
+static inline bool can_poll_ll(cycles_t end_time)
+{
+	return false;
+}
+
+#endif /* CONFIG_NET_LL_RX_POLL */
+#endif /* _LINUX_NET_LL_POLL_H */

include/net/sock.h

@@ -229,6 +229,7 @@ struct cg_proto;
   *	@sk_omem_alloc: "o" is "option" or "other"
   *	@sk_wmem_queued: persistent queue size
   *	@sk_forward_alloc: space allocated forward
+  *	@sk_napi_id: id of the last napi context to receive data for sk
   *	@sk_allocation: allocation mode
   *	@sk_sndbuf: size of send buffer in bytes
   *	@sk_flags: %SO_LINGER (l_onoff), %SO_BROADCAST, %SO_KEEPALIVE,
@@ -324,6 +325,9 @@ struct sock {
 	int			sk_forward_alloc;
 #ifdef CONFIG_RPS
 	__u32			sk_rxhash;
+#endif
+#ifdef CONFIG_NET_LL_RX_POLL
+	unsigned int		sk_napi_id;
 #endif
 	atomic_t		sk_drops;
 	int			sk_rcvbuf;

include/uapi/linux/snmp.h

@@ -253,6 +253,7 @@ enum
 	LINUX_MIB_TCPFASTOPENLISTENOVERFLOW,	/* TCPFastOpenListenOverflow */
 	LINUX_MIB_TCPFASTOPENCOOKIEREQD,	/* TCPFastOpenCookieReqd */
 	LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES, /* TCPSpuriousRtxHostQueues */
+	LINUX_MIB_LOWLATENCYRXPACKETS,		/* LowLatencyRxPackets */
 	__LINUX_MIB_MAX
 };
 

net/Kconfig

@@ -243,6 +243,18 @@ config NETPRIO_CGROUP
 	  Cgroup subsystem for use in assigning processes to network priorities on
 	  a per-interface basis
 
+config NET_LL_RX_POLL
+	bool "Low Latency Receive Poll"
+	depends on X86_TSC
+	default n
+	---help---
+	  Support Low Latency Receive Queue Poll.
+	  (For network card drivers which support this option.)
+	  When waiting for data in read or poll call directly into the the device driver
+	  to flush packets which may be pending on the device queues into the stack.
+
+	  If unsure, say N.
+
 config BQL
 	boolean
 	depends on SYSFS

net/core/datagram.c

@@ -56,6 +56,7 @@
 #include <net/sock.h>
 #include <net/tcp_states.h>
 #include <trace/events/skb.h>
+#include <net/ll_poll.h>
 
 /*
  *	Is a socket 'connection oriented' ?
@@ -207,6 +208,9 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
 		}
 		spin_unlock_irqrestore(&queue->lock, cpu_flags);
 
+		if (sk_valid_ll(sk) && sk_poll_ll(sk, flags & MSG_DONTWAIT))
+			continue;
+
 		/* User doesn't want to wait */
 		error = -EAGAIN;
 		if (!timeo)

net/core/dev.c

@@ -129,6 +129,7 @@
 #include <linux/inetdevice.h>
 #include <linux/cpu_rmap.h>
 #include <linux/static_key.h>
+#include <linux/hashtable.h>
 
 #include "net-sysfs.h"
 
@@ -166,6 +167,12 @@ static struct list_head offload_base __read_mostly;
 DEFINE_RWLOCK(dev_base_lock);
 EXPORT_SYMBOL(dev_base_lock);
 
+/* protects napi_hash addition/deletion and napi_gen_id */
+static DEFINE_SPINLOCK(napi_hash_lock);
+
+static unsigned int napi_gen_id;
+static DEFINE_HASHTABLE(napi_hash, 8);
+
 seqcount_t devnet_rename_seq;
 
 static inline void dev_base_seq_inc(struct net *net)
@@ -4136,6 +4143,58 @@ void napi_complete(struct napi_struct *n)
 }
 EXPORT_SYMBOL(napi_complete);
 
+/* must be called under rcu_read_lock(), as we dont take a reference */
+struct napi_struct *napi_by_id(unsigned int napi_id)
+{
+	unsigned int hash = napi_id % HASH_SIZE(napi_hash);
+	struct napi_struct *napi;
+
+	hlist_for_each_entry_rcu(napi, &napi_hash[hash], napi_hash_node)
+		if (napi->napi_id == napi_id)
+			return napi;
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(napi_by_id);
+
+void napi_hash_add(struct napi_struct *napi)
+{
+	if (!test_and_set_bit(NAPI_STATE_HASHED, &napi->state)) {
+
+		spin_lock(&napi_hash_lock);
+
+		/* 0 is not a valid id, we also skip an id that is taken
+		 * we expect both events to be extremely rare
+		 */
+		napi->napi_id = 0;
+		while (!napi->napi_id) {
+			napi->napi_id = ++napi_gen_id;
+			if (napi_by_id(napi->napi_id))
+				napi->napi_id = 0;
+		}
+
+		hlist_add_head_rcu(&napi->napi_hash_node,
+			&napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
+
+		spin_unlock(&napi_hash_lock);
+	}
+}
+EXPORT_SYMBOL_GPL(napi_hash_add);
+
+/* Warning : caller is responsible to make sure rcu grace period
+ * is respected before freeing memory containing @napi
+ */
+void napi_hash_del(struct napi_struct *napi)
+{
+	spin_lock(&napi_hash_lock);
+
+	if (test_and_clear_bit(NAPI_STATE_HASHED, &napi->state))
+		hlist_del_rcu(&napi->napi_hash_node);
+
+	spin_unlock(&napi_hash_lock);
+}
+EXPORT_SYMBOL_GPL(napi_hash_del);
+
 void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
 		    int (*poll)(struct napi_struct *, int), int weight)
 {

net/core/skbuff.c

@@ -733,6 +733,10 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
 	new->vlan_tci		= old->vlan_tci;
 
 	skb_copy_secmark(new, old);
+
+#ifdef CONFIG_NET_LL_RX_POLL
+	new->napi_id	= old->napi_id;
+#endif
 }
 
 /*

net/core/sock.c

@@ -139,6 +139,8 @@
 #include <net/tcp.h>
 #endif
 
+#include <net/ll_poll.h>
+
 static DEFINE_MUTEX(proto_list_mutex);
 static LIST_HEAD(proto_list);
 
@@ -2284,6 +2286,10 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 
 	sk->sk_stamp = ktime_set(-1L, 0);
 
+#ifdef CONFIG_NET_LL_RX_POLL
+	sk->sk_napi_id		=	0;
+#endif
+
 	/*
 	 * Before updating sk_refcnt, we must commit prior changes to memory
 	 * (Documentation/RCU/rculist_nulls.txt for details)

net/core/sysctl_net_core.c

@@ -19,6 +19,7 @@
 #include <net/ip.h>
 #include <net/sock.h>
 #include <net/net_ratelimit.h>
+#include <net/ll_poll.h>
 
 static int one = 1;
 
@@ -284,6 +285,15 @@ static struct ctl_table net_core_table[] = {
 		.proc_handler	= flow_limit_table_len_sysctl
 	},
 #endif /* CONFIG_NET_FLOW_LIMIT */
+#ifdef CONFIG_NET_LL_RX_POLL
+	{
+		.procname	= "low_latency_poll",
+		.data		= &sysctl_net_ll_poll,
+		.maxlen		= sizeof(unsigned long),
+		.mode		= 0644,
+		.proc_handler	= proc_doulongvec_minmax
+	},
+#endif
 #endif /* CONFIG_NET */
 	{
 		.procname	= "netdev_budget",

net/ipv4/proc.c

@@ -273,6 +273,7 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TCPFastOpenListenOverflow", LINUX_MIB_TCPFASTOPENLISTENOVERFLOW),
 	SNMP_MIB_ITEM("TCPFastOpenCookieReqd", LINUX_MIB_TCPFASTOPENCOOKIEREQD),
 	SNMP_MIB_ITEM("TCPSpuriousRtxHostQueues", LINUX_MIB_TCPSPURIOUS_RTX_HOSTQUEUES),
+	SNMP_MIB_ITEM("LowLatencyRxPackets", LINUX_MIB_LOWLATENCYRXPACKETS),
 	SNMP_MIB_SENTINEL
 };
 

net/ipv4/tcp.c

@@ -279,6 +279,7 @@
 
 #include <asm/uaccess.h>
 #include <asm/ioctls.h>
+#include <net/ll_poll.h>
 
 int sysctl_tcp_fin_timeout __read_mostly = TCP_FIN_TIMEOUT;
 
@@ -1553,6 +1554,10 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	struct sk_buff *skb;
 	u32 urg_hole = 0;
 
+	if (sk_valid_ll(sk) && skb_queue_empty(&sk->sk_receive_queue)
+	    && (sk->sk_state == TCP_ESTABLISHED))
+		sk_poll_ll(sk, nonblock);
+
 	lock_sock(sk);
 
 	err = -ENOTCONN;

net/ipv4/tcp_ipv4.c

@@ -75,6 +75,7 @@
 #include <net/netdma.h>
 #include <net/secure_seq.h>
 #include <net/tcp_memcontrol.h>
+#include <net/ll_poll.h>
 
 #include <linux/inet.h>
 #include <linux/ipv6.h>
@@ -1993,6 +1994,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	if (sk_filter(sk, skb))
 		goto discard_and_relse;
 
+	sk_mark_ll(sk, skb);
 	skb->dev = NULL;
 
 	bh_lock_sock_nested(sk);

net/ipv4/udp.c

@@ -109,6 +109,7 @@
 #include <trace/events/udp.h>
 #include <linux/static_key.h>
 #include <trace/events/skb.h>
+#include <net/ll_poll.h>
 #include "udp_impl.h"
 
 struct udp_table udp_table __read_mostly;
@@ -1709,7 +1710,10 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	sk = __udp4_lib_lookup_skb(skb, uh->source, uh->dest, udptable);
 
 	if (sk != NULL) {
-		int ret = udp_queue_rcv_skb(sk, skb);
+		int ret;
+
+		sk_mark_ll(sk, skb);
+		ret = udp_queue_rcv_skb(sk, skb);
 		sock_put(sk);
 
 		/* a return value > 0 means to resubmit the input, but

net/ipv6/tcp_ipv6.c

@@ -63,6 +63,7 @@
 #include <net/inet_common.h>
 #include <net/secure_seq.h>
 #include <net/tcp_memcontrol.h>
+#include <net/ll_poll.h>
 
 #include <asm/uaccess.h>
 
@@ -1498,6 +1499,7 @@ static int tcp_v6_rcv(struct sk_buff *skb)
 	if (sk_filter(sk, skb))
 		goto discard_and_relse;
 
+	sk_mark_ll(sk, skb);
 	skb->dev = NULL;
 
 	bh_lock_sock_nested(sk);

net/ipv6/udp.c

@@ -46,6 +46,7 @@
 #include <net/ip6_checksum.h>
 #include <net/xfrm.h>
 #include <net/inet6_hashtables.h>
+#include <net/ll_poll.h>
 
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
@@ -841,7 +842,10 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	 */
 	sk = __udp6_lib_lookup_skb(skb, uh->source, uh->dest, udptable);
 	if (sk != NULL) {
-		int ret = udpv6_queue_rcv_skb(sk, skb);
+		int ret;
+
+		sk_mark_ll(sk, skb);
+		ret = udpv6_queue_rcv_skb(sk, skb);
 		sock_put(sk);
 
 		/* a return value > 0 means to resubmit the input, but

net/socket.c

@@ -104,6 +104,12 @@
 #include <linux/route.h>
 #include <linux/sockios.h>
 #include <linux/atalk.h>
+#include <net/ll_poll.h>
+
+#ifdef CONFIG_NET_LL_RX_POLL
+unsigned long sysctl_net_ll_poll __read_mostly;
+EXPORT_SYMBOL_GPL(sysctl_net_ll_poll);
+#endif
 
 static int sock_no_open(struct inode *irrelevant, struct file *dontcare);
 static ssize_t sock_aio_read(struct kiocb *iocb, const struct iovec *iov,