From e78c3496790ee8a36522a838b59b388e8a709e65 Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Sat, 16 Aug 2014 13:40:10 -0400 Subject: time, signal: Protect resource use statistics with seqlock Both times() and clock_gettime(CLOCK_PROCESS_CPUTIME_ID) have scalability issues on large systems, due to both functions being serialized with a lock. The lock protects against reporting a wrong value, due to a thread in the task group exiting, its statistics reporting up to the signal struct, and that exited task's statistics being counted twice (or not at all). Protecting that with a lock results in times() and clock_gettime() being completely serialized on large systems. This can be fixed by using a seqlock around the events that gather and propagate statistics. As an additional benefit, the protection code can be moved into thread_group_cputime(), slightly simplifying the calling functions. In the case of posix_cpu_clock_get_task() things can be simplified a lot, because the calling function already ensures that the task sticks around, and the rest is now taken care of in thread_group_cputime(). This way the statistics reporting code can run lockless. Signed-off-by: Rik van Riel Signed-off-by: Peter Zijlstra (Intel) Cc: Alex Thorlton Cc: Andrew Morton Cc: Daeseok Youn Cc: David Rientjes Cc: Dongsheng Yang Cc: Geert Uytterhoeven Cc: Guillaume Morin Cc: Ionut Alexa Cc: Kees Cook Cc: Linus Torvalds Cc: Li Zefan Cc: Michal Hocko Cc: Michal Schmidt Cc: Oleg Nesterov Cc: Vladimir Davydov Cc: umgwanakikbuti@gmail.com Cc: fweisbec@gmail.com Cc: srao@redhat.com Cc: lwoodman@redhat.com Cc: atheurer@redhat.com Link: http://lkml.kernel.org/r/20140816134010.26a9b572@annuminas.surriel.com Signed-off-by: Ingo Molnar --- include/linux/sched.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include') diff --git a/include/linux/sched.h b/include/linux/sched.h index 5c2c885ee52b..dd9eb4807389 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -645,6 +645,7 @@ struct signal_struct { * Live threads maintain their own counters and add to these * in __exit_signal, except for the group leader. */ + seqlock_t stats_lock; cputime_t utime, stime, cutime, cstime; cputime_t gtime; cputime_t cgtime; -- cgit v1.2.3