Re: [PATCH RFC] perf/x86/amd/lbr: Don't freeze the LBR on PMI for user-only filters

[Ravi Bangoria <ravi.bangoria@amd.com>]

>>>> heh, so we basically either
>>>>
>>>> a) opt-in freeze with *new config*, but do it *only for non-kernel LBR*
>>>>
>>>> or
>>>>
>>>> b) opt-out freeze *only for non-kernel LBR* _unconditionally_, but
>>>> without adding any new config
>>>>
>>>> In both cases we have a behavior that makes sense in practice, but a)
>>>> adds some new config, while b) doesn't add anything. End result is the
>>>> same, just more configuration and need to change user space code to
>>>> opt-out the freeze.
>>>>
>>>> Is a) worth it, or we should stick to b) and keep it simple, Sandipan?
>>
>> Have you run a PGO experiment with the patch, and does it show a
>> benefit? Also, have you seen any regression in any benchmarks? If
>> no-freeze regresses some of them, we may need to give the user an
>> option to keep the freeze enabled. No?
> 
> One of Meta teams internally reported that disabling freezing
> unconditionally through the kernel command line showed a lot of
> benefit in terms of data consistency, and I don't believe any sort of
> regression was reported.
> 
> If anything, that same team is asking to unconditionally disable
> freezing fleet-wide, and this work by Puranjay is an attempt to have
> some middle ground where we don't have to do this all-or-nothing
> disablement through the kernel command line.

Sounds good, in that case, we can proceed with Puranjay's original patch.

Thanks,
Ravi