Re: [PATCH v1 12/13] perf tools: improve error handling of AMD Branch Sampling

[Kim Phillips]

On 9/9/21 2:56 AM, Stephane Eranian wrote:
> This patch improves the error message printed by perf when perf_event_open()
> fails on AMD Zen3 when using the branch sampling feature. In the case of
> EINVAL, there are two main reasons: frequency mode or period is smaller than
> the depth of the branch sampling buffer (16). The patch checks the parameters
> of the call and tries to print a relevant message to explain the error:
>
> $ perf record -b -e cpu/branch-brs/ -c 10 ls
> Error:
> AMD Branch Sampling does not support sampling period smaller than what is reported in /sys/devices/cpu/caps/branches.
>
> $ perf record -b -e cpu/branch-brs/ ls
> Error:
> AMD Branch Sampling does not support frequency mode sampling, must pass a fixed sampling period via -c option or cpu/branch-brs,period=xxxx/.
>
> Signed-off-by: Stephane Eranian <eranian@xxxxxxxxxx>
> ---

Hi Stephane,

I've rewritten this patch based on Arnaldo's comments to the previous 
(11/13) patch.  The new version attached depends on this 2-patch series:

https://lore.kernel.org/lkml/20211004214114.188477-1-kim.phillips@xxxxxxx/T/#mc4c9c582e3816ab31af6d0187e6803de1a98ac84

Thanks,

Kim