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

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Message-ID: <38c39ea6-21df-44e9-96e7-6f6fd35822a7@linux.ibm.com>
Date: Wed, 27 Mar 2024 11:34:54 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Ingo Molnar <mingo@...nel.org>
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



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


> 
> OK, I missed that, but I don't really like patch #3 of that other series, 
> so we'll need to address that first.
> 

That will be a standalone patch now and can go later based on the discussions. 

> Thanks,
> 
> 	Ingo