Messages in this thread | | | Date | Fri, 1 May 2020 12:23:37 +0200 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf evsel: Get group fd from CPU0 for system wide event |
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On Thu, Apr 30, 2020 at 09:34:51AM +0800, Jin Yao wrote: > A metric may consist of system wide event and non system-wide event. > The event group leader may be the system wide event. > > For example, the metric "C2_Pkg_Residency" consists of > "cstate_pkg/c2-residency" and "msr/tsc". The former counts on the first > CPU of socket (tagged system-wide) and the latter is per CPU. > > But "C2_Pkg_Residency" hits assertion failure on cascadelakex. > > # perf stat -M "C2_Pkg_Residency" -a -- sleep 1 > perf: util/evsel.c:1464: get_group_fd: Assertion `!(fd == -1)' failed. > Aborted > > get_group_fd(evsel, cpu, thread) > { > leader = evsel->leader; > fd = FD(leader, cpu, thread); > BUG_ON(fd == -1); > } > > Considering this case, leader is "cstate_pkg/c2-residency", evsel is > "msr/tsc" and cpu is 1. Because "cstate_pkg/c2-residency" is a system-wide > event and it's processed on CPU0, so FD(leader, 1, thread) must return an > invalid fd, then BUG_ON() may be triggered. > > This patch gets group fd from CPU0 for system wide event if > FD(leader, cpu, thread) returns invalid fd. > > With this patch, > > # perf stat -M "C2_Pkg_Residency" -a -- sleep 1 > > Performance counter stats for 'system wide': > > 1000850802 cstate_pkg/c2-residency/ # 0.5 C2_Pkg_Residency > 201446161592 msr/tsc/ > > 1.010637051 seconds time elapsed > > Fixes: 6a4bb04caacc ("perf tools: Enable grouping logic for parsed events") > Signed-off-by: Jin Yao <yao.jin@linux.intel.com> > --- > tools/perf/util/evsel.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c > index 6a571d322bb2..cd6470f63d6f 100644 > --- a/tools/perf/util/evsel.c > +++ b/tools/perf/util/evsel.c > @@ -1461,6 +1461,9 @@ static int get_group_fd(struct evsel *evsel, int cpu, int thread) > BUG_ON(!leader->core.fd); > > fd = FD(leader, cpu, thread); > + if (fd == -1 && leader->core.system_wide)
fd does not need to be -1 in here.. in my setup cstate_pkg/c2-residency/ has cpumask 0, so other cpus never get open and are 0, and the whole thing ends up with:
sys_perf_event_open: pid -1 cpu 1 group_fd 0 flags 0 sys_perf_event_open failed, error -9
I actualy thought we put -1 to fd array but couldn't find it.. perhaps we should od that
> + fd = FD(leader, 0, thread); > +
so how do we group following events?
cstate_pkg/c2-residency/ - cpumask 0 msr/tsc/ - all cpus
cpu 0 is fine.. the rest I have no idea ;-)
that's why metrics use the :W, that disables grouping on failure
jirka
> BUG_ON(fd == -1); > > return fd; > -- > 2.17.1 >
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