Subject: Re: [PATCH V2 1/2] powerpc, perf: Ignore separate BHRB privilege state filter request

From: Michael Neuling <[email-masked]>
Date: Thu, 06 Jun 2013 14:56:00 +1000

Anshuman Khandual <[email-masked]> wrote:

> Completely ignore BHRB privilege state filter request as we are
> already configuring that with privilege state filtering attribute
> for the accompanying PMU event. This would help achieve cleaner
> user space interaction for BHRB.
> 
> This patch fixes a situation like this
> 
> Before patch:-
> ------------
> ./perf record -j any -e branch-misses:k ls
> Error:
> The sys_perf_event_open() syscall returned with 95 (Operation not supported) for event (branch-misses:k).
> /bin/dmesg may provide additional information.
> No CONFIG_PERF_EVENTS=y kernel support configured?
> 
> Here 'perf record' actually copies over ':k' filter request into BHRB
> privilege state filter config and our previous check in kernel would
> fail that.
> 
> After patch:-
> -------------
> ./perf record -j any -e branch-misses:k ls
> perf  perf.data  perf.data.old  test-mmap-ring
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.002 MB perf.data (~102 samples) ]
> 
> Signed-off-by: Anshuman Khandual <[email-masked]>
> ---
>  arch/powerpc/perf/power8-pmu.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/perf/power8-pmu.c b/arch/powerpc/perf/power8-pmu.c
> index f7d1c4f..3a58416 100644
> --- a/arch/powerpc/perf/power8-pmu.c
> +++ b/arch/powerpc/perf/power8-pmu.c
> @@ -525,16 +525,12 @@ static u64 power8_bhrb_filter_map(u64 branch_sample_type)
>  	u64 pmu_bhrb_filter = 0;
>  	u64 br_privilege = branch_sample_type & ONLY_PLM;
>  
> -	/* BHRB and regular PMU events share the same prvillege state
> +	/* BHRB and regular PMU events share the same privilege state
>  	 * filter configuration. BHRB is always recorded along with a
> -	 * regular PMU event. So privilege state filter criteria for BHRB
> -	 * and the companion PMU events has to be the same. As a default
> -	 * "perf record" tool sets all privillege bits ON when no filter
> -	 * criteria is provided in the command line. So as along as all
> -	 * privillege bits are ON or they are OFF, we are good to go.
> +	 * regular PMU event. As the privilege state filter is handled
> +	 * in the basic PMC configuration of the accompanying regular
> +	 * PMU event, we ignore any separate BHRB specific request.
>  	 */
> -	if ((br_privilege != 7) && (br_privilege != 0))
> -		return -1;

br_privilege is now unused which causes this compile error.

arch/powerpc/perf/power8-pmu.c:526:6: error: unused variable ‘br_privilege’ [-Werror=unused-variable]

I assume since you didn't compile test this code, you also didn't
runtime test it either?!!?!?!?

Mikey

>  
>  	/* No branch filter requested */
>  	if (branch_sample_type & PERF_SAMPLE_BRANCH_ANY)
> -- 
> 1.7.11.7
> 
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