Messages in this thread | | | From | Namhyung Kim <> | Date | Mon, 8 Nov 2021 10:50:54 -0800 | Subject | Re: [PATCH v3] perf evsel: Fix missing exclude_{host,guest} setting |
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On Sun, Nov 7, 2021 at 2:26 AM Ravi Bangoria <ravi.bangoria@amd.com> wrote: > > > > On 07-Nov-21 12:54 AM, Arnaldo Carvalho de Melo wrote: > > Em Fri, Nov 05, 2021 at 11:00:29AM -0700, Namhyung Kim escreveu: > >> Hello, > >> > >> On Wed, Nov 3, 2021 at 12:22 AM Ravi Bangoria <ravi.bangoria@amd.com> wrote: > >>> > >>>> The current logic for the perf missing feature has a bug that it can > >>>> wrongly clear some modifiers like G or H. Actually some PMUs don't > >>>> support any filtering or exclusion while others do. But we check it > >>>> as a global feature. > >>> > >>> (Sorry to pitch in bit late) > >>> > >>> AMD has one more problem on a similar line. On AMD, non-precise and > >>> precise sampling are provided by core and IBS pmu respectively. Plus, > >>> core pmu has filtering capability but IBS does not. Perf by default > >>> sets precise_ip=3 and exclude_guest=1 and goes on decreasing precise_ip > >>> with exclude_guest set until perf_event_open() succeeds. This is > >>> causing perf to always fallback to core pmu (non-precise mode) even if > >>> it's perfectly feasible to do precise sampling. Do you guys think this > >>> problem should also be addressed while designing solution for Namhyung's > >>> patch or solve it seperately like below patch: > >>> > >>> ---><--- > >>> > >>> From 48808299679199c39ff737a30a7f387669314fd7 Mon Sep 17 00:00:00 2001 > >>> From: Ravi Bangoria <ravi.bangoria@amd.com> > >>> Date: Tue, 2 Nov 2021 11:01:12 +0530 > >>> Subject: [PATCH] perf/amd/ibs: Don't set exclude_guest by default > >>> > >>> Perf tool sets exclude_guest by default while calling perf_event_open(). > >>> Because IBS does not have filtering capability, it always gets rejected > >>> by IBS PMU driver and thus perf falls back to non-precise sampling. Fix > >>> it by not setting exclude_guest by default on AMD. > >>> > >>> Before: > >>> $ sudo ./perf record -C 0 -vvv true |& grep precise > >>> precise_ip 3 > >>> decreasing precise_ip by one (2) > >>> precise_ip 2 > >>> decreasing precise_ip by one (1) > >>> precise_ip 1 > >>> decreasing precise_ip by one (0) > >>> > >>> After: > >>> $ sudo ./perf record -C 0 -vvv true |& grep precise > >>> precise_ip 3 > >>> decreasing precise_ip by one (2) > >>> precise_ip 2 > >>> > >>> Reported-by: Kim Phillips <kim.phillips@amd.com> > >>> Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com> > >> > >> It'd be nice if it can cover explicit -e cycles:pp as well. Anyway, > > > > Ravi, please consider Namhyung's request, a patch on top as I'm adding > > this already. > > For explicit :pp modifier, evsel->precise_max does not get set and thus perf > does not try with different attr->precise_ip values while exclude_guest set. > So no issue with explicit :pp: > > $ sudo ./perf record -C 0 -e cycles:pp -vvv |& grep "precise_ip\|exclude_guest" > precise_ip 2 > exclude_guest 1 > precise_ip 2 > exclude_guest 1 > switching off exclude_guest, exclude_host > precise_ip 2 > ^C > > Also, with :P modifier, evsel->precise_max gets set but exclude_guest does > not and thus :P also works fine: > > $ sudo ./perf record -C 0 -e cycles:P -vvv |& grep "precise_ip\|exclude_guest" > precise_ip 3 > decreasing precise_ip by one (2) > precise_ip 2 > ^C
Ah, ok. Thanks for making it clear!
Thanks, Namhyung
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