Messages in this thread | | | Subject | Re: [PATCH] perf/tests: Fix test case 95 on s390 and use same event | From | German Gomez <> | Date | Thu, 28 Jul 2022 13:28:51 +0100 |
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On 28/07/2022 13:20, Thomas Richter wrote: > On 7/28/22 11:25, German Gomez wrote: >> Thanks for the fix, Thomas >> >> On 27/07/2022 15:14, Thomas Richter wrote: >>> On linux-next tree perf test 95 was added recently. >>> s390 does not support branch sampling at all and the test case fails >>> despite for checking branch support before hand. >>> The check for support of branching >>> uses the software event named dummy, as seen in the line: >>> >>> perf record -b -o- -e dummy -B true > /dev/null 2>&1 || exit 2 >> Just curious, do you know why the command succeeds in this platform (and >> potentially others)? >> >> I got the idea of using "dummy" from [1] but only tested on arm64 and >> x86. I thought the platforms would reject it if -b was not implemented >> regardless of the event. Did I misunderstand the use of dummy? >> >> Thanks, >> German >> >> [1] https://lore.kernel.org/all/20220617073840.GA45710@leoy-ThinkPad-X240s/ >> > Well, dummy is a predefined event of type software, you see that when you add > some -v options as in > # perf record -e dummy -vvv > DEBUGINFOD_URLS= > Using CPUID IBM,3931,704,A01,3.7,002f > nr_cblocks: 0 > affinity: SYS > mmap flush: 1 > comp level: 0 > ------------------------------------------------------------ > perf_event_attr: > type 1 <----------- type 1 is software > size 128 > config 0x9 > { sample_period, sample_freq } 4000 > > > So this event is never sent to an hardware PMU (which would have type 0) and thus > mostly succeeds where as the perf record command without event uses default > event cycles. And that one is sent to hardware PMU on s390...
Thanks for explaining! My bad for missing this.
Acked-by: German Gomez <german.gomez@arm.com>
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