linux-kernel - Re: [External] : Re: [REGRESSION][v6.17-rc1]sched/fair: Bump sd->max_newidle_lb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <f6379aa6-459d-4205-96ea-9848e55d7f9c@arm.com>
Date: Thu, 30 Oct 2025 21:53:50 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Peter Zijlstra <peterz@...radead.org>,
 Adam Li <adamli@...amperecomputing.com>
Cc: Joseph Salisbury <joseph.salisbury@...cle.com>, Chris Mason
 <clm@...a.com>, clm@...com, Vincent Guittot <vincent.guittot@...aro.org>,
 Juri Lelli <juri.lelli@...hat.com>, Ingo Molnar <mingo@...hat.com>,
 Steven Rostedt <rostedt@...dmis.org>, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [External] : Re: [REGRESSION][v6.17-rc1]sched/fair: Bump
 sd->max_newidle_lb_cost when newidle balance fails

On 30.10.25 10:30, Peter Zijlstra wrote:
> 
> Hi Adam,
> 
> On Thu, Oct 30, 2025 at 03:22:34PM +0800, Adam Li wrote:
> 
>> Commit 155213a2aed4 brings ~6% regression for SpecJBB critical-jOPS on
>> AmpereOne server. 
>>
>> Baseline: v6.17 kernel + patch. Compared with baseline:
>> NI_TARGET	+7%
>> NI_SPARE	-3%
>> NI_RUNNABLE	-4%
>> NI_RANDOM	-3%
>>
>> So NI_TARGET reverts the performance regression.
>> The other options brings more regression for SpecJBB.
> 
> Excellent, how does NI_TARGET+NI_RANDOM work for you? Like Chris, I
> found that the schbench workload was really suffering from doing too
> many idle balance attempts that weren't really working out.
> 
> NI_RANDOM reduces the number of newidle balances based on the success
> ratio. Eg. if you have successful balancing 25% of the time, it will do
> 1 in 4 balances and count a successful balance as 4 to keep the
> accounting straight.
> 
> So workloads with a high success rate will keep newidle balance calls
> frequent, while workloads with a low success rate (like schbench) will
> greatly reduce the number of calls.

Results with OLTP 'hammerdb - mysqld' on Arm64 VMs

				NOPM		P50 latency

6.18-rc3			baseline	baseline

6.18-rc3-revert-155213a2aed4	+12%		-8.5%

6.18-rc3 NI_TARGET		+12%		-8.2%

6.18-rc3 NI_SPARE		+-0%		+-0%

6.18-rc3 NI_RUNNABLE		-1%		+1%

6.18-rc3 NI_RANDOM	        -1%		+1%

Looks like only NI_TARGET reverts the regression here.