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authorEric Dumazet <eric.dumazet@gmail.com>2011-05-24 11:12:58 +0200
committerThomas Gleixner <tglx@linutronix.de>2011-05-24 12:10:51 +0200
commit8af088710d1eb3c980e0ef3779c8d47f3f217b48 (patch)
treee122a2e65684f0a40d263ba73afe3d54a2c5993a /include/linux/posix-timers.h
parentd762f4383100c2a87b1a3f2d678cd3b5425655b4 (diff)
posix-timers: RCU conversion
Ben Nagy reported a scalability problem with KVM/QEMU that hit very hard a single spinlock (idr_lock) in posix-timers code, on its 48 core machine. Even on a 16 cpu machine (2x4x2), a single test can show 98% of cpu time used in ticket_spin_lock, from lock_timer Ref: http://www.spinics.net/lists/kvm/msg51526.html Switching to RCU is quite easy, IDR being already RCU ready. idr_lock should be locked only for an insert/delete, not a lookup. Benchmark on a 2x4x2 machine, 16 processes calling timer_gettime(). Before : real 1m18.669s user 0m1.346s sys 1m17.180s After : real 0m3.296s user 0m1.366s sys 0m1.926s Reported-by: Ben Nagy <ben@iagu.net> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Tested-by: Ben Nagy <ben@iagu.net> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Avi Kivity <avi@redhat.com> Cc: John Stultz <johnstul@us.ibm.com> Cc: Richard Cochran <richard.cochran@omicron.at> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'include/linux/posix-timers.h')
-rw-r--r--include/linux/posix-timers.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 808227d40a6..959c14132f4 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -82,6 +82,7 @@ struct k_itimer {
unsigned long expires;
} mmtimer;
struct alarm alarmtimer;
+ struct rcu_head rcu;
} it;
};