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

Mohamed Abuelfotoh, Hazem
2026-02-04T12:46:06Z

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@noisy.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