Commit cba1aab8 authored by Reinette Chatre's avatar Reinette Chatre Committed by Thomas Gleixner

x86/intel_rdt: Document new mode, size, and bit_usage

By default resource groups allow sharing of their cache allocations.  There
is nothing that prevents a resource group from configuring a cache
allocation that overlaps with that of an existing resource group.

To enable resource groups to specify that their cache allocations cannot be
shared a resource group "mode" is introduced to support two possible modes:
"shareable" and "exclusive". A "shareable" resource group allows sharing of
its cache allocations, an "exclusive" resource group does not. A new
resctrl file "mode" associated with each resource group is used to
communicate its (the associated resource group's) mode setting and allow
the mode to be changed.  The new "mode" file as well as two other resctrl
files, "bit_usage" and "size", are introduced in this series.

Add documentation for the three new resctrl files as well as one example
demonstrating their use.
Signed-off-by: default avatarReinette Chatre <reinette.chatre@intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: vikas.shivappa@linux.intel.com
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/f03a3059ec40ae719be6f3fba9f446bb055e0064.1529706536.git.reinette.chatre@intel.com
parent 32206ab3
......@@ -65,6 +65,27 @@ related to allocation:
some platforms support devices that have their
own settings for cache use which can over-ride
these bits.
"bit_usage": Annotated capacity bitmasks showing how all
instances of the resource are used. The legend is:
"0" - Corresponding region is unused. When the system's
resources have been allocated and a "0" is found
in "bit_usage" it is a sign that resources are
wasted.
"H" - Corresponding region is used by hardware only
but available for software use. If a resource
has bits set in "shareable_bits" but not all
of these bits appear in the resource groups'
schematas then the bits appearing in
"shareable_bits" but no resource group will
be marked as "H".
"X" - Corresponding region is available for sharing and
used by hardware and software. These are the
bits that appear in "shareable_bits" as
well as a resource group's allocation.
"S" - Corresponding region is used by software
and available for sharing.
"E" - Corresponding region is used exclusively by
one resource group. No sharing allowed.
Memory bandwitdh(MB) subdirectory contains the following files
with respect to allocation:
......@@ -163,6 +184,16 @@ When control is enabled all CTRL_MON groups will also contain:
A list of all the resources available to this group.
Each resource has its own line and format - see below for details.
"size":
Mirrors the display of the "schemata" file to display the size in
bytes of each allocation instead of the bits representing the
allocation.
"mode":
The "mode" of the resource group dictates the sharing of its
allocations. A "shareable" resource group allows sharing of its
allocations while an "exclusive" resource group does not.
When monitoring is enabled all MON groups will also contain:
"mon_data":
......@@ -502,7 +533,71 @@ siblings and only the real time threads are scheduled on the cores 4-7.
# echo F0 > p0/cpus
4) Locking between applications
Example 4
---------
The resource groups in previous examples were all in the default "shareable"
mode allowing sharing of their cache allocations. If one resource group
configures a cache allocation then nothing prevents another resource group
to overlap with that allocation.
In this example a new exclusive resource group will be created on a L2 CAT
system with two L2 cache instances that can be configured with an 8-bit
capacity bitmask. The new exclusive resource group will be configured to use
25% of each cache instance.
# mount -t resctrl resctrl /sys/fs/resctrl/
# cd /sys/fs/resctrl
First, we observe that the default group is configured to allocate to all L2
cache:
# cat schemata
L2:0=ff;1=ff
We could attempt to create the new resource group at this point, but it will
fail because of the overlap with the schemata of the default group:
# mkdir p0
# echo 'L2:0=0x3;1=0x3' > p0/schemata
# cat p0/mode
shareable
# echo exclusive > p0/mode
-sh: echo: write error: Invalid argument
# cat info/last_cmd_status
schemata overlaps
To ensure that there is no overlap with another resource group the default
resource group's schemata has to change, making it possible for the new
resource group to become exclusive.
# echo 'L2:0=0xfc;1=0xfc' > schemata
# echo exclusive > p0/mode
# grep . p0/*
p0/cpus:0
p0/mode:exclusive
p0/schemata:L2:0=03;1=03
p0/size:L2:0=262144;1=262144
A new resource group will on creation not overlap with an exclusive resource
group:
# mkdir p1
# grep . p1/*
p1/cpus:0
p1/mode:shareable
p1/schemata:L2:0=fc;1=fc
p1/size:L2:0=786432;1=786432
The bit_usage will reflect how the cache is used:
# cat info/L2/bit_usage
0=SSSSSSEE;1=SSSSSSEE
A resource group cannot be forced to overlap with an exclusive resource group:
# echo 'L2:0=0x1;1=0x1' > p1/schemata
-sh: echo: write error: Invalid argument
# cat info/last_cmd_status
overlaps with exclusive group
Locking between applications
----------------------------
Certain operations on the resctrl filesystem, composed of read/writes
to/from multiple files, must be atomic.
......@@ -510,7 +605,7 @@ to/from multiple files, must be atomic.
As an example, the allocation of an exclusive reservation of L3 cache
involves:
1. Read the cbmmasks from each directory
1. Read the cbmmasks from each directory or the per-resource "bit_usage"
2. Find a contiguous set of bits in the global CBM bitmask that is clear
in any of the directory cbmmasks
3. Create a new directory
......
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