diff options
author | Yunlong Song | 2015-03-31 21:46:29 +0800 |
---|---|---|
committer | Arnaldo Carvalho de Melo | 2015-04-08 09:07:21 -0300 |
commit | a35e27d0e5d801ff75481a8f639bb4d59ea1aafa (patch) | |
tree | 02e8b4e62a5baf5f7ff876fd0de0ca2a9c20991b /tools/perf | |
parent | 0755bc4dc77a876aa60d4b3d33b5f6506f21f91b (diff) |
perf sched replay: Increase the MAX_PID value to fix assertion failure problem
Current MAX_PID is only 65536, which will cause assertion failure problem
when CPU cores are more than 64 in x86_64.
This is because the pid_max value in x86_64 is at least
PIDS_PER_CPU_DEFAULT * num_possible_cpus() (see function pidmap_init
defined in kernel/pid.c), where PIDS_PER_CPU_DEFAULT is 1024 (defined in
include/linux/threads.h).
Thus for MAX_PID = 65536, the correspoinding CPU cores are
65536/1024=64. This is obviously not enough at all for x86_64, and will
cause an assertion failure problem due to BUG_ON(pid >= MAX_PID) in the
codes.
We increase MAX_PID value from 65536 to 1024*1000, which can be used in
x86_64 with 1000 cores.
This number is finally decided according to the limitation of stack size
of calling process.
Use 'ulimit -a', the result shows the stack size of any process is 8192
Kbytes, which is defined in include/uapi/linux/resource.h (#define
_STK_LIM (8*1024*1024)).
Thus we choose a large enough value for MAX_PID, and make it satisfy to
the limitation of the stack size, i.e., making the perf process take up
a memory space just smaller than 8192 Kbytes.
We have calculated and tested that 1024*1000 is OK for MAX_PID.
This means perf sched replay can now be used with at most 1000 cores in
x86_64 without any assertion failure problem.
Example:
Test environment: x86_64 with 160 cores
$ cat /proc/sys/kernel/pid_max
163840
Before this patch:
$ perf sched replay
run measurement overhead: 240 nsecs
sleep measurement overhead: 55379 nsecs
the run test took 1000004 nsecs
the sleep test took 1059424 nsecs
perf: builtin-sched.c:330: register_pid: Assertion `!(pid >= 65536)'
failed.
Aborted
After this patch:
$ perf sched replay
run measurement overhead: 221 nsecs
sleep measurement overhead: 55397 nsecs
the run test took 999920 nsecs
the sleep test took 1053313 nsecs
nr_run_events: 10
nr_sleep_events: 1562
nr_wakeup_events: 5
task 0 ( :1: 1), nr_events: 1
task 1 ( :2: 2), nr_events: 1
task 2 ( :3: 3), nr_events: 1
task 3 ( :5: 5), nr_events: 1
...
Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1427809596-29559-3-git-send-email-yunlong.song@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/perf')
-rw-r--r-- | tools/perf/builtin-sched.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c index a1893e8dfe17..c46610447ede 100644 --- a/tools/perf/builtin-sched.c +++ b/tools/perf/builtin-sched.c @@ -28,7 +28,7 @@ #define MAX_CPUS 4096 #define COMM_LEN 20 #define SYM_LEN 129 -#define MAX_PID 65536 +#define MAX_PID 1024000 struct sched_atom; |