linux-kernel - Re: [PATCH 4/4] sched/fair: Proportional newidle balance

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Message-ID: <af193dee-bf32-430e-86f7-2f996ba71013@amazon.com>
Date: Wed, 4 Feb 2026 12:45:41 +0000
From: "Mohamed Abuelfotoh, Hazem" <abuehaze@...zon.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: Mario Roy <marioeroy@...il.com>, Chris Mason <clm@...a.com>, "Joseph
 Salisbury" <joseph.salisbury@...cle.com>, Adam Li
	<adamli@...amperecomputing.com>, Josh Don <joshdon@...gle.com>,
	<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>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] sched/fair: Proportional newidle balance

On 02/02/2026 11:07, Mohamed Abuelfotoh, Hazem wrote:
> On 02/02/2026 10:51, Peter Zijlstra wrote:
>>
>> OK, that clarifies.
>>
>> How does the NI_RATE patch work for you?
>>
>>    https://lkml.kernel.org/ 
>> r/20260127151748.GA1079264@...sy.programming.kicks-ass.net
> 
> Sure I am going to apply this patch and report the results.
> 
> 
> 
I have tested the patch proposed in [1] on top of v6.12.66 and 
unfortunately I haven't seen any improvement. I mainly compared the 
results between v6.12.66 & v6.12.66_revert_1b9c118fe318 which has the 
revert for 1b9c118fe318 ("sched/fair: Proportional newidle balance") and 
v6.12.66_proposed which is v6.12.66 + the patch proposed in [1]. I 
mainly focused on AMD based c7a.4xlarge which was highly impacted as 
previously discussed in this thread. The baseline is 
v6.12.66_revert_1b9c118fe318 as it showed the best performance among the 
other available kernel options.

Version           | Benchmark name   | SUT EC2 Instance| diff %
v6.12.66          | postgresql       | c7a.4xlarge     | -4.0%
v6.12.66          | nginx_lb         | c7a.4xlarge     | -5.0%
v6.12.66          | memcached        | c7a.4xlarge     | -11.0%
v6.12.66_proposed | postgresql       | c7a.4xlarge     | -4.0%
v6.12.66_proposed | nginx_lb         | c7a.4xlarge     | -5.0%
v6.12.66_proposed | memcached        | c7a.4xlarge     | -13.0%


Furthermore We have also seen around 10-20% randwrite fio performance 
regression on v6.18.5 only on AMD based VMs. We confirmed that this 
regression is caused by 1b9c118fe318 ("sched/fair: Proportional newidle 
balance"). We are currently testing if the patch proposed in [1] to see 
if it will help with this regression and will be sharing the results & 
reproduction steps and environment in the next update.


[1 
https://lkml.kernel.org/r/20260127151748.GA1079264@noisy.programming.kicks-ass.net