[PATCH 4/9] perf sched replay: Realloc the memory of pid_to_task stepwise to adapt to the different pid_max configurations

From: Yunlong Song
Date: Tue Mar 31 2015 - 09:45:18 EST


Although the memory of pid_to_task can be allocated via calloc according
to the value of /proc/sys/kernel/pid_max, it cannot handle the case when
pid_max is changed after 'perf sched record' has created its perf.data.
If the new pid_max configured in 'perf sched replay' is smaller than the
old pid_max configured in 'perf sched record', then it will cause the
assertion failure problem. To solve this problem, we realloc the memory
of pid_to_task stepwise once the passed-in pid parameter in register_pid
is larger than the current pid_max.

Example:

Test environment: x86_64 with 160 cores

$ cat /proc/sys/kernel/pid_max
163840
$ perf sched record ls
$ echo 5000 > /proc/sys/kernel/pid_max
$ cat /proc/sys/kernel/pid_max
5000

Before this patch:

$ perf sched replay
run measurement overhead: 221 nsecs
sleep measurement overhead: 55356 nsecs
the run test took 1000011 nsecs
the sleep test took 1060940 nsecs
perf: builtin-sched.c:337: register_pid: Assertion `!(pid >= (unsigned
long)pid_max)' failed.
Aborted

After this patch:

$ perf sched replay
run measurement overhead: 221 nsecs
sleep measurement overhead: 55611 nsecs
the run test took 1000026 nsecs
the sleep test took 1060486 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@xxxxxxxxxx>
---
tools/perf/builtin-sched.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 20d887b..dd71481 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -334,7 +334,12 @@ static struct task_desc *register_pid(struct perf_sched *sched,
pid_max = MAX_PID;
BUG_ON((sched->pid_to_task = calloc(pid_max, sizeof(struct task_desc *))) == NULL);
}
- BUG_ON(pid >= (unsigned long)pid_max);
+ if (pid >= (unsigned long)pid_max) {
+ BUG_ON((sched->pid_to_task = realloc(sched->pid_to_task, (pid + 1) *
+ sizeof(struct task_desc *))) == NULL);
+ while (pid >= (unsigned long)pid_max)
+ sched->pid_to_task[pid_max++] = NULL;
+ }

task = sched->pid_to_task[pid];

--
1.8.5.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/