Re: [report] Performance regressions introduced via "cpuidle: menu: Remove iowait influence" on 6.12.y

[Christian Loehle <christian.loehle@arm.com>]

On 12/24/25 12:18, ALOK TIWARI wrote:
> Hi Christian,
> 
> 
> On 12/3/2025 11:01 PM, ALOK TIWARI wrote:
>> Hi,
>>
>> I’m reporting a performance regression of up to 6% sequential I/O
>> vdbench regression observed on 6.12.y kernel.
>> While running performance benchmarks on v6.12.60 kernel the sequential I/O vdbench metrics are showing a 5-6% performance regression when compared to v6.12.48
>>
>> Bisect root cause commit
>> ========================
>> - commit b39b62075ab4 ("cpuidle: menu: Remove iowait influence")
>>
>> Things work fine again when the previously removed performance- multiplier code is added back.
>>
>> Test details
>> ============
>> The system is connected to a number of disks in disk array using multipathing and directio configuration in the vdbench profile.
>>
>> wd=wd1,sd=sd*,rdpct=0,seekpct=sequential,xfersize=128k
>> rd=128k64T,wd=wd1,iorate=max,elapsed=600,interval=1,warmup=300,threads=64
>>
>>
>> Thanks,
>> Alok
>>
> 
> Just a gentle ping in case this was missed.
> Please let us know if we are missing anything or if there are additional things to consider.
> 

Hi Alok,
indeed it was missed, sorry!
The cpuidle sysfs dumps pre and post test would be interesting like so:
cat /sys/devices/system/cpu/cpu*/cpuidle/state*/*
for both would be helpful so I can see what actually changed.
Or a trace with cpu_idle events.
Additionally a latency distribution of the IO requests would be helpful to relate
them to the cpuidle wakeups.

Thanks,
Christian