* [PATCH] sched/doc: Update documentation for base_slice_ns and CONFIG_HZ relation
@ 2024-03-20 17:38 Mukesh Kumar Chaurasiya
2024-03-21 14:55 ` Randy Dunlap
0 siblings, 1 reply; 2+ messages in thread
From: Mukesh Kumar Chaurasiya @ 2024-03-20 17:38 UTC (permalink / raw
To: linux-doc; +Cc: corbet, mingo, linux-kernel, Mukesh Kumar Chaurasiya
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>
---
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 6cffffe26500..82985d675554 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 the CONFIG_HZ leads to base_slice_ns < TICK_NSEC. The settings 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
--
2.44.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] sched/doc: Update documentation for base_slice_ns and CONFIG_HZ relation
2024-03-20 17:38 [PATCH] sched/doc: Update documentation for base_slice_ns and CONFIG_HZ relation Mukesh Kumar Chaurasiya
@ 2024-03-21 14:55 ` Randy Dunlap
0 siblings, 0 replies; 2+ messages in thread
From: Randy Dunlap @ 2024-03-21 14:55 UTC (permalink / raw
To: Mukesh Kumar Chaurasiya, linux-doc; +Cc: corbet, mingo, linux-kernel
Hi,
On 3/20/24 10:38, Mukesh Kumar Chaurasiya wrote:
> 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>
> ---
> 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 6cffffe26500..82985d675554 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 the CONFIG_HZ leads to base_slice_ns < TICK_NSEC. The settings of
TICK_NSEC, the {setting, value}
> +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
--
#Randy
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