Re: IPC drop down on AMD epyc 7702P

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Vincent,

On 5/5/2025 8:40 PM, Vincent Guittot wrote:
>>> commit 16b0a7a1a0af  ("sched/fair: Ensure tasks spreading in LLC
>>> during LB") eases the spread of task inside a LLC so It's not obvious
>>> for me how it would increase "a lot of CPU migrations go out of CCX,
>>> then L3 miss,". On the other hand, it will spread task in SMT and in
>>> LLC which can prevent running at highest freq on some system but I
>>> don't know if it's relevant for this SoC.
>>
>> I misspoke there. JB's workload seems to be sensitive even to core to
>> core migrations - "relax_domain_level=2" actually disabled newidle
>> balance above CLUSTER level which is a subset of MC on x86 and gets
> 
> Did he try with relax_domain_level=3, i.e. prevent newilde idle
> balance between LLC ? I don't see results showing that it's not enough
> to prevent newly idle migration between LLC

I don't think he did. JB if it isn't too much trouble, could you please
try running with "relax_domain_level=3" in kernel cmdline and see if
the performance is similar to "relax_domain_level=2".

I only realized it later that "relax_domain_level" works on topology
levels before degeneration.

-- 
Thanks and Regards,
Prateek