Hi Jiri,
On 5/9/2020 3:37 PM, Jin, Yao wrote:
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
I think I get the root cause. That should be a serious bug in get_group_fd,
access violation!
For a group mixed with system-wide event and per-core event and the group leader is system-wide
event, access violation will happen.
perf_evsel__alloc_fd allocates one FD member for system-wide event (only
FD(evsel, 0, 0) is valid).
But for per core event, perf_evsel__alloc_fd allocates N FD members (N = ncpus). For example, for
ncpus is 8, FD(evsel, 0, 0) to FD(evsel, 7, 0) are valid.
get_group_fd(struct evsel *evsel, int cpu, int thread)
{
struct evsel *leader = evsel->leader;
fd = FD(leader, cpu, thread); /* access violation may happen here */
}
If leader is system-wide event, only the FD(leader, 0, 0) is valid.
When get_group_fd accesses FD(leader, 1, 0), access violation happens.
My fix is:
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 28683b0eb738..db05b8a1e1a8 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1440,6 +1440,9 @@ static int get_group_fd(struct evsel *evsel, int cpu, int
thread)
if (evsel__is_group_leader(evsel))
return -1;
+ if (leader->core.system_wide && !evsel->core.system_wide)
+ return -2;
+
/*
* Leader must be already processed/open,
* if not it's a bug.
@@ -1665,6 +1668,11 @@ static int evsel__open_cpu(struct evsel *evsel, struct
perf_cpu_map *cpus,
pid = perf_thread_map__pid(threads, thread);
group_fd = get_group_fd(evsel, cpu, thread);
+ if (group_fd == -2) {
+ errno = EINVAL;
+ err = -EINVAL;
+ goto out_close;
+ }
retry_open:
test_attr__ready();
It enables the perf_evlist__reset_weak_group. And in the second_pass (in __run_perf_stat), the
events will be opened successfully.
I have tested OK for this fix on cascadelakex.
Thanks
Jin Yao
