Messages in this thread | | | Subject | Re: [PATCH] perf evsel: Get group fd from CPU0 for system wide event | From | "Jin, Yao" <> | Date | Sat, 2 May 2020 10:33:59 +0800 |
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Hi Jiri,
On 5/1/2020 6:23 PM, Jiri Olsa wrote: > 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 > >
I have tested on two platforms. On KBL desktop fd is 0 for this case, but on oncascadelakex server, fd is -1, so the BUG_ON(fd == -1) is triggered.
>> + fd = FD(leader, 0, thread); >> + > > so how do we group following events? > > cstate_pkg/c2-residency/ - cpumask 0 > msr/tsc/ - all cpus >
Not sure if it's enough to only use cpumask 0 because cstate_pkg/c2-residency/ should be per-socket.
> cpu 0 is fine.. the rest I have no idea ;-) >
Perhaps we directly remove the BUG_ON(fd == -1) assertion?
Thanks Jin Yao
> 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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