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| author | Mukesh Kumar Chaurasiya <mchauras@linux.ibm.com> | 2024-03-20 23:08:16 +0530 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2024-03-21 20:34:16 +0100 |
| commit | a26979377bf34534ce5ee2712d2a46157ec61498 (patch) | |
| tree | 0fb4ad7262eb7667aa5839977f7ac33dbabb759b | |
| parent | 4ae3dc83b047d51485cce1a72be277a110d77c91 (diff) | |
sched/doc: Update documentation for base_slice_ns and CONFIG_HZ relation
The tunable base_slice_ns is dependent on CONFIG_HZ (i.e. TICK_NSEC)
for any significant performance improvement. The reason being the
scheduler tick is not frequent enough to force preemption when
base_slice expires in case of:
base_slice_ns < TICK_NSEC
The below data is of stress-ng:
Number of CPU: 1
Stressor threads: 4
Time: 30sec
On CONFIG_HZ=1000
| base_slice | avg-run (msec) | context-switches |
| ---------- | -------------- | ---------------- |
| 3ms | 2.914 | 10342 |
| 6ms | 4.857 | 6196 |
| 9ms | 6.754 | 4482 |
| 12ms | 7.872 | 3802 |
| 22ms | 11.294 | 2710 |
| 32ms | 13.425 | 2284 |
On CONFIG_HZ=100
| base_slice | avg-run (msec) | context-switches |
| ---------- | -------------- | ---------------- |
| 3ms | 9.144 | 3337 |
| 6ms | 9.113 | 3301 |
| 9ms | 8.991 | 3315 |
| 12ms | 12.935 | 2328 |
| 22ms | 16.031 | 1915 |
| 32ms | 18.608 | 1622 |
base_slice: the value of base_slice in ms
avg-run (msec): average time of the stressor threads got on cpu before
it got preempted
context-switches: number of context switches for the stress-ng process
Signed-off-by: Mukesh Kumar Chaurasiya <mchauras@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20240320173815.927637-2-mchauras@linux.ibm.com
| -rw-r--r-- | Documentation/scheduler/sched-design-CFS.rst | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/Documentation/scheduler/sched-design-CFS.rst b/Documentation/scheduler/sched-design-CFS.rst index 6cffffe26500..e030876fbd68 100644 --- a/Documentation/scheduler/sched-design-CFS.rst +++ b/Documentation/scheduler/sched-design-CFS.rst @@ -100,6 +100,9 @@ which can be used to tune the scheduler from "desktop" (i.e., low latencies) to "server" (i.e., good batching) workloads. It defaults to a setting suitable for desktop workloads. SCHED_BATCH is handled by the CFS scheduler module too. +In case CONFIG_HZ results in base_slice_ns < TICK_NSEC, the value of +base_slice_ns will have little to no impact on the workloads. + Due to its design, the CFS scheduler is not prone to any of the "attacks" that exist today against the heuristics of the stock scheduler: fiftyp.c, thud.c, chew.c, ring-test.c, massive_intr.c all work fine and do not impact |