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

From: Michael Neuling <[email-masked]>
Date: Fri, 07 Jun 2013 09:46:54 +1000

Anshuman Khandual <[email-masked]> wrote:

> On 06/06/2013 10:26 AM, Michael Neuling wrote:
> > 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?!!?!?!?
> 
> 
> Always compile with the cross compiler "ARCH=powerpc
> CROSS_COMPILE=powerpc64-linux-gnu- make" I copied over
> arch/powerpc/config/pseries_defconfig and compiled it. Some how it
> missed to be a 64 bit kernel config which resulted in shutting down
> compilation of arch/powerpc/perf/power8-pmu.c file. So never
> encountered this compiler warning message before. Will fix this.

I don't understand this at all... pseries_defconfig is a 64bit kernel.

BTW. you don't need to copy it.  Just do "make pseries_defconfig && make
vmlinux".

Mikey