Re: [PATCH 1/4] perf/amd/ibs: Add load/store SW filters to IBS OP PMU

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

Hi Ingo, Namhyung,

>>> An alternate approach is mem_op BPF filter:
>>>
>>>   perf record --filter "mem_op == load || mem_op == store" ...
>>>
>>> However, there are few issues with it:
>>> o BPF filter is called after preparing entire perf sample. If the sample
>>>   does not satisfy the filtering criteria, all the efforts of preparing
>>>   perf sample gets wasted.
>>
>> Could we add an 'early' BPF callback point as well, to fast-discard 
>> samples?
> 
> I guess that would require a new BPF program type than PERF_EVENT and
> handle driver-specific details.

Right.

>>> o BPF filter requires root privilege.
>>
>> Could we add 'built-in', 'safe' BPF scripts that are specifically 
>> prepared for perf events filtering purposes, that can be toggled by 
>> non-root users as well? These could be toggled by tooling via sysfs or 
>> so, or even via the perf syscall if that turns out to be the better 
>> approach.
> 
> We have BPF filter framework in the perf tools and it can be run as
> normal user.  But root user should load and pin the BPF program prior
> to use like below.
> 
>   $ sudo perf record --setup-filter pin
> 
>   $ perf record -d -e ibs_op/swfilt/u --filter 'mem_op == load' ...

Thanks Namhyung.

Ingo, Do you feel the idea of perf specific 'safe' BPF script is still
worth pursuing despite similar functionality is already provided by
--setup-filter?

Thanks,
Ravi