Re: [REGRESSION] 'perf mem record' on a Intel hybrid system broken

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2024-12-11 1:48 p.m., Namhyung Kim wrote:
> On Wed, Dec 11, 2024 at 12:55:03PM -0500, Liang, Kan wrote:
>> On 2024-12-04 2:24 p.m., Namhyung Kim wrote:
>>> I think I got a related report from the kernel test robot but it was a
>>> Sapphire Rapids machine.  I don't have a Intel hybrid machine in hand.
>>> I'll try to take a look at it on Sapphire Rapids.
>>
>> The default precise_ip level for perf mem is always 3.
>>
>> For the latest intel platforms, it implies PDist, which is only
>> available on GP 0.
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/events/intel/core.c#n4412
>>
>> However, the mem-load PEBS event is available on all GP counters but GP
>> 0. :(
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/events/intel/ds.c#n1176
>>
>> So the precise_ip-- is required.
>>
>> The failure of scheduling returns -EINVAL.
>>
>> But Namhyung's patch assumes that the kernel return -EOPNOTSUPP when PMU
>> doesn't support the given precise level.
>> (Sorry, I didn't notice the case early.)
>>
>> Is it possible to reduce the precise_ip for the -EINVAL as well?
> 
> Sure, please see https://lore.kernel.org/r/Z1DV0lN8qHSysX7f@google.com
>

Thanks for the fix. It looks good to me.

Reviewed-by: Kan Liang <kan.liang@linux.intel.com>

Thanks,
Kan