Subject: Re: [PATCH] powerpc/perf: Fix task context setting for trace imc

From: Michael Ellerman <[email-masked]>
Date: Wed, 19 Jan 2022 21:56:12 +1100

Athira Rajeev <[email-masked]> writes:
> Trace IMC (In-Memory collection counters) in powerpc is
> useful for application level profiling. For trace_imc,
> presently task context (task_ctx_nr) is set to
> perf_hw_context. But perf_hw_context is to be used for
> cpu PMU. So for trace_imc, even though it is per thread
> PMU, it is preferred to use sw_context inorder to be able
> to do application level monitoring. Hence change the
> task_ctx_nr to use perf_sw_context.

It's not a software event though, so this is not obviously correct.

Can you explain more why this is OK, I guess perf_sw_context is misnamed
these days? And can you add a comment in the code explaining why this
hardware PMU is using perf_sw_context.

cheers

> Fixes: 012ae244845f ("powerpc/perf: Trace imc PMU functions")
> Signed-off-by: Athira Rajeev <[email-masked]>
> Reviewed-by: Madhavan Srinivasan <[email-masked]>
> ---
>  arch/powerpc/perf/imc-pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c
> index e106909ff9c3..f3b3262bdf02 100644
> --- a/arch/powerpc/perf/imc-pmu.c
> +++ b/arch/powerpc/perf/imc-pmu.c
> @@ -1457,7 +1457,7 @@ static int trace_imc_event_init(struct perf_event *event)
>  
>  	event->hw.idx = -1;
>  
> -	event->pmu->task_ctx_nr = perf_hw_context;
> +	event->pmu->task_ctx_nr = perf_sw_context;
>  	event->destroy = reset_global_refc;
>  	return 0;
>  }
> -- 
> 2.33.0