Messages in this thread | | | Subject | Re: [PATCH] perf evsel: Get group fd from CPU0 for system wide event | From | "Jin, Yao" <> | Date | Sat, 9 May 2020 15:37:19 +0800 |
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Hi Jiri,
On 5/5/2020 8:03 AM, Jiri Olsa wrote: > On Sat, May 02, 2020 at 10:33:59AM +0800, Jin, Yao wrote: > > SNIP > >>>> @@ -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? > > I think we need to make clear how to deal with grouping over > events that comes for different cpus > > so how do we group following events? > > cstate_pkg/c2-residency/ - cpumask 0 > msr/tsc/ - all cpus > > > what's the reason/expected output of groups with above events? > seems to make sense only if we limit msr/tsc/ to cpumask 0 as well > > jirka >
On 2-socket machine (e.g cascadelakex), "cstate_pkg/c2-residency/" is per-socket event and the cpumask is 0 and 24.
root@lkp-csl-2sp5 /sys/devices/cstate_pkg# cat cpumask 0,24
We can't limit it to cpumask 0. It should be programmed on CPU0 and CPU24 (the first CPU on each socket).
The "msr/tsc" are per-cpu event, it should be programmed on all cpus. So I don't think we can limit msr/tsc to cpumask 0.
The issue is how we deal with get_group_fd().
static int get_group_fd(struct evsel *evsel, int cpu, int thread) { struct evsel *leader = evsel->leader; int fd;
if (evsel__is_group_leader(evsel)) return -1;
/* * Leader must be already processed/open, * if not it's a bug. */ BUG_ON(!leader->core.fd);
fd = FD(leader, cpu, thread); BUG_ON(fd == -1);
return fd; }
When evsel is "msr/tsc/",
FD(leader, 0, 0) is 3 (3 is the fd of "cstate_pkg/c2-residency/" on CPU0) FD(leader, 1, 0) is -1 BUG_ON asserted.
If we just return group_fd(-1) for "msr/tsc", it looks like it's not a problem, is it?
Thanks Jin Yao
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