- 19 May, 2021 1 commit
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Yejune Deng authored
is_percpu_thread() more elegantly handles SMP vs UP, and further checks the presence of PF_NO_SETAFFINITY. This lets us catch cases where check_preemption_disabled() can race with a concurrent sched_setaffinity(). Signed-off-by:
Yejune Deng <yejune.deng@gmail.com> [Amended changelog] Signed-off-by:
Valentin Schneider <valentin.schneider@arm.com> Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210510151024.2448573-3-valentin.schneider@arm.com
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- 18 May, 2021 3 commits
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Valentin Schneider authored
For all intents and purposes, the idle task is a per-CPU kthread. It isn't created via the same route as other pcpu kthreads however, and as a result it is missing a few bells and whistles: it fails kthread_is_per_cpu() and it doesn't have PF_NO_SETAFFINITY set. Fix the former by giving the idle task a kthread struct along with the KTHREAD_IS_PER_CPU flag. This requires some extra iffery as init_idle() call be called more than once on the same idle task. Signed-off-by:
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Mel Gorman authored
Update sysctl/kernel.rst. Signed-off-by:
Mel Gorman <mgorman@suse.de> Signed-off-by:
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Peter Zijlstra authored
There's no point doing delta==0 updates. Suggested-by:
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- 13 May, 2021 1 commit
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Paul Gortmaker authored
We have a mismatch between RCU and isolation -- in relation to what is considered the maximum valid CPU number. This matters because nohz_full= and rcu_nocbs= are joined at the hip; in fact the former will enforce the latter. So we don't want a CPU mask to be valid for one and denied for the other. The difference 1st appeared as of v4.15; further details are below. As it is confusing to anyone who isn't looking at the code regularly, a reminder is in order; three values exist here: CONFIG_NR_CPUS - compiled in maximum cap on number of CPUs supported. nr_cpu_ids - possible # of CPUs (typically reflects what ACPI says) cpus_present - actual number of present/detected/installed CPUs. For this example, I'll refer to NR_CPUS=64 from "make defconfig" and nr_cpu_ids=6 for ACPI reporting on a board that could run a six core, and present=4 for a quad that is physically in the socket. From dmesg: smpboot: Allowing 6 CPUs, 2 hotplug CPUs setup_percpu: NR_CPUS:64 nr_cpumask_bits:64 nr_cpu_ids:6 nr_node_ids:1 rcu: RCU restricting CPUs from NR_CPUS=64 to nr_cpu_ids=6. smp: Brought up 1 node, 4 CPUs And from userspace, see: paul@trash:/sys/devices/system/cpu$ cat present 0-3 paul@trash:/sys/devices/system/cpu$ cat possible 0-5 paul@trash:/sys/devices/system/cpu$ cat kernel_max 63 Everything is fine if we boot 5x5 for rcu/nohz: Command line: BOOT_IMAGE=/boot/bzImage nohz_full=2-5 rcu_nocbs=2-5 root=/dev/sda1 ro NO_HZ: Full dynticks CPUs: 2-5. rcu: Offload RCU callbacks from CPUs: 2-5. ..even though there is no CPU 4 or 5. Both RCU and nohz_full are OK. Now we push that > 6 but less than NR_CPU and with 15x15 we get: Command line: BOOT_IMAGE=/boot/bzImage rcu_nocbs=2-15 nohz_full=2-15 root=/dev/sda1 ro rcu: Note: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs. rcu: Offload RCU callbacks from CPUs: 2-5. These are both functionally equivalent, as we are only changing flags on phantom CPUs that don't exist, but note the kernel interpretation changes. And worse, it only changes for one of the two - which is the problem. RCU doesn't care if you want to restrict the flags on phantom CPUs but clearly nohz_full does after this change from v4.15. edb93821: ("sched/isolation: Move isolcpus= handling to the housekeeping code") - if (cpulist_parse(str, non_housekeeping_mask) < 0) { - pr_warn("Housekeeping: Incorrect nohz_full cpumask\n"); + err = cpulist_parse(str, non_housekeeping_mask); + if (err < 0 || cpumask_last(non_housekeeping_mask) >= nr_cpu_ids) { + pr_warn("Housekeeping: nohz_full= or isolcpus= incorrect CPU range\n"); To be clear, the sanity check on "possible" (nr_cpu_ids) is new here. The goal was reasonable ; not wanting housekeeping to land on a not-possible CPU, but note two things: 1) this is an exclusion list, not an inclusion list; we are tracking non_housekeeping CPUs; not ones who are explicitly assigned housekeeping 2) we went one further in 9219565a ("sched/isolation: Require a present CPU in housekeeping mask") - ensuring that housekeeping was sanity checking against present and not just possible CPUs. To be clear, this means the check added in v4.15 is doubly redundant. And more importantly, overly strict/restrictive. We care now, because the bitmap boot arg parsing now knows that a value of "N" is NR_CPUS; the size of the bitmap, but the bitmap code doesn't know anything about the subtleties of our max/possible/present CPU specifics as outlined above. So drop the check added in v4.15 (edb93821) and make RCU and nohz_full both in alignment again on NR_CPUS so "N" works for both, and then they can fall back to nr_cpu_ids internally just as before. Command line: BOOT_IMAGE=/boot/bzImage nohz_full=2-N rcu_nocbs=2-N root=/dev/sda1 ro NO_HZ: Full dynticks CPUs: 2-5. rcu: Offload RCU callbacks from CPUs: 2-5. As shown above, with this change, RCU and nohz_full are in sync, even with the use of the "N" placeholder. Same result is achieved with "15". Signed-off-by:
Paul Gortmaker <paul.gortmaker@windriver.com> Signed-off-by:
Ingo Molnar <mingo@kernel.org> Acked-by:
Paul E. McKenney <paulmck@kernel.org> Link: https://lore.kernel.org/r/20210419042659.1134916-1-paul.gortmaker@windriver.com
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- 12 May, 2021 35 commits
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Alexey Dobriyan authored
Make: struct dl_rq::dl_nr_migratory struct dl_rq::dl_nr_running struct rt_rq::rt_nr_boosted struct rt_rq::rt_nr_migratory struct rt_rq::rt_nr_total struct rq::nr_uninterruptible 32-bit. If total number of tasks can't exceed 2**32 (and less due to futex pid limits), then per-runqueue counters can't as well. This patchset has been sponsored by REX Prefix Eradication Society. Signed-off-by:
Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by:
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Alexey Dobriyan authored
Runqueue ->nr_iowait counters are 32-bit anyway. Propagate 32-bitness into other code, but don't try too hard. Signed-off-by:
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Alexey Dobriyan authored
Creating 2**32 tasks to wait in D-state is impossible and wasteful. Return "unsigned int" and save on REX prefixes. Signed-off-by:
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Alexey Dobriyan authored
Creating 2**32 tasks is impossible due to futex pid limits and wasteful anyway. Nobody has done it. Bring nr_running() into 32-bit world to save on REX prefixes. Signed-off-by:
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Ingo Molnar authored
A few more snuck in. Also capitalize 'CPU' while at it. Signed-off-by: -
Valentin Schneider authored
As pointed out by commit de9b8f5d ("sched: Fix crash trying to dequeue/enqueue the idle thread") init_idle() can and will be invoked more than once on the same idle task. At boot time, it is invoked for the boot CPU thread by sched_init(). Then smp_init() creates the threads for all the secondary CPUs and invokes init_idle() on them. As the hotplug machinery brings the secondaries to life, it will issue calls to idle_thread_get(), which itself invokes init_idle() yet again. In this case it's invoked twice more per secondary: at _cpu_up(), and at bringup_cpu(). Given smp_init() already initializes the idle tasks for all *possible* CPUs, no further initialization should be required. Now, removing init_idle() from idle_thread_get() exposes some interesting expectations with regards to the idle task's preempt_count: the secondary startup always issues a preempt_disable(), requiring some reset of the preempt count to 0 between hot-unplug and hotplug, which is currently served by idle_thread_get() -> idle_init(). Given the idle task is supposed to have preemption disabled once and never see it re-enabled, it seems that what we actually want is to initialize its preempt_count to PREEMPT_DISABLED and leave it there. Do that, and remove init_idle() from idle_thread_get(). Secondary startups were patched via coccinelle: @begone@ @@ -preempt_disable(); ... cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); Signed-off-by:
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Chris Hyser authored
Provides a selftest and examples of using the interface. [peterz: updated to not use sched_debug] Signed-off-by:
Chris Hyser <chris.hyser@oracle.com> Signed-off-by:
Don Hiatt <dhiatt@digitalocean.com> Tested-by:
Hongyu Ning <hongyu.ning@linux.intel.com> Tested-by:
Vincent Guittot <vincent.guittot@linaro.org> Link: https://lkml.kernel.org/r/20210422123309.100860030@infradead.org
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Chris Hyser authored
This patch provides support for setting and copying core scheduling 'task cookies' between threads (PID), processes (TGID), and process groups (PGID). The value of core scheduling isn't that tasks don't share a core, 'nosmt' can do that. The value lies in exploiting all the sharing opportunities that exist to recover possible lost performance and that requires a degree of flexibility in the API. From a security perspective (and there are others), the thread, process and process group distinction is an existent hierarchal categorization of tasks that reflects many of the security concerns about 'data sharing'. For example, protecting against cache-snooping by a thread that can just read the memory directly isn't all that useful. With this in mind, subcommands to CREATE/SHARE (TO/FROM) provide a mechanism to create and share cookies. CREATE/SHARE_TO specify a target pid with enum pidtype used to specify the scope of the targeted tasks. For example, PIDTYPE_TGID will share the cookie with the process and all of it's threads as typically desired in a security scenario. API: prctl(PR_SCHED_CORE, PR_SCHED_CORE_GET, tgtpid, pidtype, &cookie) prctl(PR_SCHED_CORE, PR_SCHED_CORE_CREATE, tgtpid, pidtype, NULL) prctl(PR_SCHED_CORE, PR_SCHED_CORE_SHARE_TO, tgtpid, pidtype, NULL) prctl(PR_SCHED_CORE, PR_SCHED_CORE_SHARE_FROM, srcpid, pidtype, NULL) where 'tgtpid/srcpid == 0' implies the current process and pidtype is kernel enum pid_type {PIDTYPE_PID, PIDTYPE_TGID, PIDTYPE_PGID, ...}. For return values, EINVAL, ENOMEM are what they say. ESRCH means the tgtpid/srcpid was not found. EPERM indicates lack of PTRACE permission access to tgtpid/srcpid. ENODEV indicates your machines lacks SMT. [peterz: complete rewrite] Signed-off-by: -
Peter Zijlstra authored
Note that sched_core_fork() is called from under tasklist_lock, and not from sched_fork() earlier. This avoids a few races later. Signed-off-by:
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Peter Zijlstra authored
In order to not have to use pid_struct, create a new, smaller, structure to manage task cookies for core scheduling. Signed-off-by:
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Aubrey Li authored
- Don't migrate if there is a cookie mismatch Load balance tries to move task from busiest CPU to the destination CPU. When core scheduling is enabled, if the task's cookie does not match with the destination CPU's core cookie, this task may be skipped by this CPU. This mitigates the forced idle time on the destination CPU. - Select cookie matched idle CPU In the fast path of task wakeup, select the first cookie matched idle CPU instead of the first idle CPU. - Find cookie matched idlest CPU In the slow path of task wakeup, find the idlest CPU whose core cookie matches with task's cookie Signed-off-by:Aubrey Li <aubrey.li@linux.intel.com> Signed-off-by:
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Peter Zijlstra authored
When a sibling is forced-idle to match the core-cookie; search for matching tasks to fill the core. rcu_read_unlock() can incur an infrequent deadlock in sched_core_balance(). Fix this by using the RCU-sched flavor instead. Signed-off-by:
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Joel Fernandes (Google) authored
During force-idle, we end up doing cross-cpu comparison of vruntimes during pick_next_task. If we simply compare (vruntime-min_vruntime) across CPUs, and if the CPUs only have 1 task each, we will always end up comparing 0 with 0 and pick just one of the tasks all the time. This starves the task that was not picked. To fix this, take a snapshot of the min_vruntime when entering force idle and use it for comparison. This min_vruntime snapshot will only be used for cross-CPU vruntime comparison, and nothing else. A note about the min_vruntime snapshot and force idling: During selection: When we're not fi, we need to update snapshot. when we're fi and we were not fi, we must update snapshot. When we're fi and we were already fi, we must not update snapshot. Which gives: fib fi update 0 0 1 0 1 1 1 0 1 1 1 0 Where: fi: force-idled now fib: force-idled before So the min_vruntime snapshot needs to be updated when: !(fib && fi). Also, the cfs_prio_less() function needs to be aware of whether the core is in force idle or not, since it will be use this information to know whether to advance a cfs_rq's min_vruntime_fi in the hierarchy. So pass this information along via pick_task() -> prio_less(). Suggested-by:
Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by:
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Joel Fernandes (Google) authored
The rationale is as follows. In the core-wide pick logic, even if need_sync == false, we need to go look at other CPUs (non-local CPUs) to see if they could be running RT. Say the RQs in a particular core look like this: Let CFS1 and CFS2 be 2 tagged CFS tags. Let RT1 be an untagged RT task. rq0 rq1 CFS1 (tagged) RT1 (no tag) CFS2 (tagged) Say schedule() runs on rq0. Now, it will enter the above loop and pick_task(RT) will return NULL for 'p'. It will enter the above if() block and see that need_sync == false and will skip RT entirely. The end result of the selection will be (say prio(CFS1) > prio(CFS2)): rq0 rq1 CFS1 IDLE When it should have selected: rq0 rq1 IDLE RT Suggested-by:
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Vineeth Pillai authored
If there is only one long running local task and the sibling is forced idle, it might not get a chance to run until a schedule event happens on any cpu in the core. So we check for this condition during a tick to see if a sibling is starved and then give it a chance to schedule. Signed-off-by:
Vineeth Pillai <viremana@linux.microsoft.com> Signed-off-by:
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Peter Zijlstra authored
Instead of only selecting a local task, select a task for all SMT siblings for every reschedule on the core (irrespective which logical CPU does the reschedule). Signed-off-by:
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Peter Zijlstra authored
Introduce task_struct::core_cookie as an opaque identifier for core scheduling. When enabled; core scheduling will only allow matching task to be on the core; where idle matches everything. When task_struct::core_cookie is set (and core scheduling is enabled) these tasks are indexed in a second RB-tree, first on cookie value then on scheduling function, such that matching task selection always finds the most elegible match. NOTE: *shudder* at the overhead... NOTE: *sigh*, a 3rd copy of the scheduling function; the alternative is per class tracking of cookies and that just duplicates a lot of stuff for no raisin (the 2nd copy lives in the rt-mutex PI code). [Joel: folded fixes] Signed-off-by:
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Peter Zijlstra authored
Because sched_class::pick_next_task() also implies sched_class::set_next_task() (and possibly put_prev_task() and newidle_balance) it is not state invariant. This makes it unsuitable for remote task selection. Signed-off-by:
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Peter Zijlstra authored
Stuff the meat of sched_core_put() into a work such that we can use sched_core_put() from atomic context. Signed-off-by:
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Peter Zijlstra authored
rq_lockp() includes a static_branch(), which is asm-goto, which is asm volatile which defeats regular CSE. This means that: if (!static_branch(&foo)) return simple; if (static_branch(&foo) && cond) return complex; Doesn't fold and we get horrible code. Introduce __rq_lockp() without the static_branch() on. Signed-off-by:
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Peter Zijlstra authored
Introduce the basic infrastructure to have a core wide rq->lock. This relies on the rq->__lock order being in increasing CPU number (inside a core). It is also constrained to SMT8 per lockdep (and SMT256 per preempt_count). Luckily SMT8 is the max supported SMT count for Linux (Mips, Sparc and Power are known to have this). Signed-off-by:
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Peter Zijlstra authored
When switching on core-sched, CPUs need to agree which lock to use for their RQ. The new rule will be that rq->core_enabled will be toggled while holding all rq->__locks that belong to a core. This means we need to double check the rq->core_enabled value after each lock acquire and retry if it changed. This also has implications for those sites that take multiple RQ locks, they need to be careful that the second lock doesn't end up being the first lock. Verify the lock pointer after acquiring the first lock, because if they're on the same core, holding any of the rq->__lock instances will pin the core state. While there, change the rq->__lock order to CPU number, instead of rq address, this greatly simplifies the next patch. Signed-off-by:
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Peter Zijlstra authored
In preparation of playing games with rq->lock, abstract the thing using an accessor. Signed-off-by:
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Peter Zijlstra authored
In prepration for playing games with rq->lock, add some rq_lock wrappers. Signed-off-by:
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Peter Zijlstra authored
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Peter Zijlstra authored
Just like sched_schedstats, allow runtime enabling (and disabling) of delayacct. This is useful if one forgot to add the delayacct boot time option. Signed-off-by:
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Peter Zijlstra authored
Assuming this stuff isn't actually used much; disable it by default and avoid allocating and tracking the task_delay_info structure. taskstats is changed to still report the regular sched and sched_info and only skip the missing task_delay_info fields instead of not reporting anything. Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Reviewed-by:
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Peter Zijlstra authored
Cheaper when delayacct is disabled. Signed-off-by:
Balbir Singh <bsingharora@gmail.com> Acked-by:
Johannes Weiner <hannes@cmpxchg.org> Link: https://lkml.kernel.org/r/20210505111525.248028369@infradead.org
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Peter Zijlstra authored
AFAICT KVM only relies on SCHED_INFO. Nothing uses the p->delays data that belongs to TASK_DELAY_ACCT. Signed-off-by:
Paolo Bonzini <pbonzini@redhat.com> Acked-by:
Marc Zyngier <maz@kernel.org> Acked-by:
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Peter Zijlstra authored
The situation around sched_info is somewhat complicated, it is used by sched_stats and delayacct and, indirectly, kvm. If SCHEDSTATS=Y (but disabled by default) sched_info_on() is unconditionally true -- this is the case for all distro kernel configs I checked. If for some reason SCHEDSTATS=N, but TASK_DELAY_ACCT=Y, then sched_info_on() can return false when delayacct is disabled, presumably because there would be no other users left; except kvm is. Instead of complicating matters further by accurately accounting sched_stat and kvm state, simply unconditionally enable when SCHED_INFO=Y, matching the common distro case. Signed-off-by:
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Peter Zijlstra authored
For consistency, rename {queued,dequeued} to {enqueue,dequeue}. Signed-off-by:Rik van Riel <riel@surriel.com> Reviewed-by:
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Peter Zijlstra authored
Like all scheduler statistics, use sched_clock() based time. Signed-off-by:
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Pierre Gondois authored
find_energy_efficient_cpu() (feec()) searches the best energy CPU to place a task on. To do so, compute_energy() estimates the energy impact of placing the task on a CPU, based on CPU and task utilization signals. Utilization signals can be concurrently updated while evaluating a performance domain (pd). In some cases, this leads to having a 'negative delta', i.e. placing the task in the pd is seen as an energy gain. Thus, any further energy comparison is biased. In case of a 'negative delta', return prev_cpu since: 1. a 'negative delta' happens in less than 0.5% of feec() calls, on a Juno with 6 CPUs (4 little, 2 big) 2. it is unlikely to have two consecutive 'negative delta' for a task, so if the first call fails, feec() will correctly place the task in the next feec() call 3. EAS current behavior tends to select prev_cpu if the task doesn't raise the OPP of its current pd. prev_cpu is EAS's generic decision 4. prev_cpu should be preferred to returning an error code. In the latter case, select_idle_sibling() would do the placement, selecting a big (and not energy efficient) CPU. As 3., the task would potentially reside on the big CPU for a long time Reported-by:
Xuewen Yan <xuewen.yan@unisoc.com> Suggested-by:
Pierre Gondois <Pierre.Gondois@arm.com> Signed-off-by:
Lukasz Luba <lukasz.luba@arm.com> Reviewed-by:
Dietmar Eggemann <dietmar.eggemann@arm.com> Reviewed-by:
Vincent Donnefort <vincent.donnefort@arm.com> Link: https://lkml.kernel.org/r/20210504090743.9688-3-Pierre.Gondois@arm.com
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Pierre Gondois authored
find_energy_efficient_cpu() searches the best energy CPU to place a task on. To do so, the energy of each performance domain (pd) is computed w/ and w/o the task placed on it. The energy of a pd w/o the task (base_energy_pd) is computed prior knowing whether a CPU is available in the pd. Move the base_energy_pd computation after looping through the CPUs of a pd and only compute it if at least one CPU is available. Suggested-by:
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Rik van Riel authored
The try_to_wake_up function has an optimization where it can queue a task for wakeup on its previous CPU, if the task is still in the middle of going to sleep inside schedule(). Once schedule() re-enables IRQs, the task will be woken up with an IPI, and placed back on the runqueue. If we have such a wakeup pending, there is no need to search other CPUs for runnable tasks. Just skip (or bail out early from) newidle balancing, and run the just woken up task. For a memcache like workload test, this reduces total CPU use by about 2%, proportionally split between user and system time, and p99 and p95 application response time by 10% on average. The schedstats run_delay number shows a similar improvement. Signed-off-by:
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