linux-kernel - Re: [PATCH v2 00/12] sched: Address schbench regression

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Message-ID: <931f8673-a2b0-4b4e-8ae8-269b5a5c235d@linux.ibm.com>
Date: Tue, 8 Jul 2025 22:59:06 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Chris Mason <clm@...a.com>, Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        vschneid@...hat.com
Subject: Re: [PATCH v2 00/12] sched: Address schbench regression



On 7/8/25 20:39, Chris Mason wrote:
> On 7/7/25 5:05 AM, Shrikanth Hegde wrote:
>>
>>
>> On 7/2/25 17:19, Peter Zijlstra wrote:
>>> Hi!
>>>
>>> Previous version:
>>>
>>>     https://lkml.kernel.org/r/20250520094538.086709102@infradead.org
>>>
>>> Changes:
>>>    - keep dl_server_stop(), just remove the 'normal' usage of it (juril)
>>>    - have the sched_delayed wake list IPIs do select_task_rq() (vingu)
>>>    - fixed lockdep splat (dietmar)
>>>    - added a few preperatory patches
>>>
>>>
>>> Patches apply on top of tip/master (which includes the disabling of
>>> private futex)
>>> and clm's newidle balance patch (which I'm awaiting vingu's ack on).
>>>
>>> Performance is similar to the last version; as tested on my SPR on
>>> v6.15 base:
>>>
>>
>>
>> Hi Peter,
>> Gave this a spin on a machine with 5 cores (SMT8) PowerPC system.
>>
>> I see significant regression in schbench. let me know if i have to test
>> different
>> number of threads based on the system size.
>> Will go through the series and will try a bisect meanwhile.
> 
> Not questioning the git bisect results you had later in this thread, but
> double checking that you had the newidle balance patch in place that
> Peter mentioned?
> 
> https://lore.kernel.org/lkml/20250626144017.1510594-2-clm@fb.com/
> 
> The newidle balance frequency changes the cost of everything else, so I
> wanted to make sure we were measuring the same things.
> 

Hi Chris.

It was base + series only. and base was 8784fb5fa2e0("Merge irq/drivers into tip/master").
So it didn't have your changes.

I tested again with your changes and i still see a major regression.


./schbench -L -m 4 -M auto -t 64 -n 0 -t 60 -i 60
Wakeup Latencies percentiles (usec) runtime 30 (s) (18848611 total samples)
	  50.0th: 115        (5721408 samples)
	  90.0th: 238        (7500535 samples)
	* 99.0th: 316        (1670597 samples)
	  99.9th: 360        (162283 samples)
	  min=1, max=1487

RPS percentiles (requests) runtime 30 (s) (31 total samples)
	  20.0th: 623616     (7 samples)
	* 50.0th: 629760     (15 samples)
	  90.0th: 631808     (7 samples)
	  min=617820, max=635475
average rps: 628514.30


git log --oneline
7aaf5ef0841b (HEAD) sched: Add ttwu_queue support for delayed tasks
f77b53b6766a sched: Change ttwu_runnable() vs sched_delayed
986ced69ba7b sched: Use lock guard in sched_ttwu_pending()
2c0eb5c88134 sched: Clean up ttwu comments
e1374ac7f74a sched: Re-arrange __ttwu_queue_wakelist()
7e673db9e90f psi: Split psi_ttwu_dequeue()
e2225f1c24a9 sched: Introduce ttwu_do_migrate()
80765734f127 sched: Add ttwu_queue controls
745406820d30 sched: Use lock guard in ttwu_runnable()
d320cebe6e28 sched: Optimize ttwu() / select_task_rq()
329fc7eaad76 sched/deadline: Less agressive dl_server handling
708281193493 sched/psi: Optimize psi_group_change() cpu_clock() usage
c28590ad7b91 sched/fair: bump sd->max_newidle_lb_cost when newidle balance fails
8784fb5fa2e0 (origin/master, origin/HEAD) Merge irq/drivers into tip/master