perf_event: Adjust frequency and unthrottle for non-group-leader events
authorPaul Mackerras <paulus@samba.org>
Wed, 14 Oct 2009 05:58:03 +0000 (16:58 +1100)
committerIngo Molnar <mingo@elte.hu>
Wed, 14 Oct 2009 06:39:32 +0000 (08:39 +0200)
commit03541f8b69c058162e4cf9675ec9181e6a204d55
tree67cd314f717b1b455861d1cfb9761162a44096b3
parenta003236c32706f3c1f74d4e3b98c58cf0d9a9d8f
perf_event: Adjust frequency and unthrottle for non-group-leader events

The loop in perf_ctx_adjust_freq checks the frequency of sampling
event counters, and adjusts the event interval and unthrottles the
event if required, and resets the interrupt count for the event.
However, at present it only looks at group leaders.

This means that a sampling event that is not a group leader will
eventually get throttled, once its interrupt count reaches
sysctl_perf_event_sample_rate/HZ --- and that is guaranteed to
happen, if the event is active for long enough, since the interrupt
count never gets reset.  Once it is throttled it never gets
unthrottled, so it basically just stops working at that point.

This fixes it by making perf_ctx_adjust_freq use ctx->event_list
rather than ctx->group_list.  The existing spin_lock/spin_unlock
around the loop makes it unnecessary to put rcu_read_lock/
rcu_read_unlock around the list_for_each_entry_rcu().

Reported-by: Mark W. Krentel <krentel@cs.rice.edu>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <19157.26731.855609.165622@cargo.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
kernel/perf_event.c