linux-kernel - Re: [PATCH v3 0/2] sched: Minor changes for rd->overload access

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Date: Thu, 28 Mar 2024 11:34:19 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: peterz@...radead.org, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, qyousef@...alina.io,
	linux-kernel@...r.kernel.org, vschneid@...hat.com
Subject: Re: [PATCH v3 0/2] sched: Minor changes for rd->overload access


* Shrikanth Hegde <sshegde@...ux.ibm.com> wrote:

> 
> 
> On 3/26/24 1:30 PM, Ingo Molnar wrote:
> > 
> > * Shrikanth Hegde <sshegde@...ux.ibm.com> wrote:
> > 
> >>
> >>
> >> On 3/25/24 4:06 PM, Ingo Molnar wrote:
> >>>
> >>> * Shrikanth Hegde <sshegde@...ux.ibm.com> wrote:
> >>>
> >>>> v2 -> v3:
> >>>> - Wrapped check for value change inside ser_rd_overload_status
> >>>>   as suggested by Qais.
> >>>> - Added reviewed-by tags.
> >>>>
> >>>> v1 -> v2:
> >>>> - dropped Fixes tag.
> >>>> - Added one of the perf probes in the changelog for reference.
> >>>> - Added reviewed-by tags.
> >>>>
> >>>> tl;dr
> >>>> When running workloads in large systems, it was observed that access to
> >>>> rd->overload was taking time. It would be better to check the value
> >>>> before updating since value changes less often. Patch 1/2 does that.
> >>>> With patch updates happen only if necessary. CPU Bus traffic reduced a
> >>>> bit. No significant gains in workload performance.
> >>>
> >>> Could you please post this against the latest scheduler tree, ie. tip:sched/core?
> >>>
> >>> Thanks,
> >>>
> >>> 	Ingo
> >>
> >> Hi Ingo. I had mentioned the same in cover letter. Sorry if I didn't 
> >> mention it in the correct place. 
> >>
> >> *These patches depend on below to be applied first*
> >> https://lore.kernel.org/all/20240307085725.444486-1-sshegde@linux.ibm.com/
> >>
> >> After that the above patch would apply.
> 
> Hi Ingo. 
> 
> These two patches apply cleanly now to sched/core. 
> 
> 7a9dd7ef946c (HEAD -> sched/core) sched/fair: Use helper functions to access rd->overload
> 4f24aa918558 sched/fair: Check rd->overload value before update
> c829d6818b60 (origin/sched/core) sched/fair: Simplify the continue_balancing logic in sched_balance_newidle()
> d0f5d3cefc25 sched/fair: Introduce is_rd_overutilized() helper function to access root_domain::overutilized

I've applied them, but note that there were quite a few avoidable typos 
and grammar mistakes in the changelogs. Please always review what 
you've submitted versus what I have applied and try to learn from that: 
I almost invariable have to edit some detail to make the changelog more 
presentable... Could you please take more care with future patches?

I also renamed the accessor functions in the second patch to:

      get_rd_overload()
      set_rd_overload()

Plus I've applied a patch to rename ::overload to ::overloaded. It is 
silly to use an ambiguous noun instead of a clear adjective when naming 
such a flag ...

Thanks,

	Ingo