Re: [RFC PATCH] sched: Rate limit migrations

[Aaron Lu]

On Tue, Apr 11, 2023 at 05:41:16PM -0400, Mathieu Desnoyers wrote:
> This WIP patch rate-limits migrations to 32 migrations per 10ms window
> for each task.
> 
> The specific migration count and window size can be changed with the
> following defines in kernel/sched/sched.h:
> 
> - SCHED_MIGRATION_WINDOW_NS
> - SCHED_MIGRATION_LIMIT
> 
> Testing is welcome, especially to see if it helps with Aaron's
> migration-heavy workload wrt rseq concurrency id performance
> regression.

Initial test shows the migration number for a 5s window is still in some
millions and profile wise, contention didn't change much, still in the
range of single digit to 20% something during 3 minutes run.

If this limit works, then the total migration number should be less
than: 224 * 2 * 3200 * 5 = 7million so hard to say if the limit works as
expected since the number I captured is indeed less than 7 million.
224 * 2 means totally there are 448 tasks, 224 client and 224
server. 3200 is the theoretical migration number for a task in a 1s
window and 5 means 5 seconds.

I'll play with it more to see how things change.