The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: a26979377bf34534ce5ee2712d2a46157ec61498
Gitweb: https://git.kernel.org/tip/a26979377bf34534ce5ee2712d2a46157ec61498
Author: Mukesh Kumar Chaurasiya <mchauras@xxxxxxxxxxxxx>
AuthorDate: Wed, 20 Mar 2024 23:08:16 +05:30
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 21 Mar 2024 20:34:16 +01:00
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@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240320173815.927637-2-mchauras@xxxxxxxxxxxxx
---
Documentation/scheduler/sched-design-CFS.rst | 3 +++
1 file changed, 3 insertions(+)
diff --git a/Documentation/scheduler/sched-design-CFS.rst b/Documentation/scheduler/sched-design-CFS.rst
index 6cffffe..e030876 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
|