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authorJason Low <[email protected]>2014-01-28 11:13:13 -0800
committerIngo Molnar <[email protected]>2014-03-11 12:14:53 +0100
commit47667fa1502e4d759df87e9cc7fbc0f202483361 (patch)
treed2355a95e004334147e00650ec4d638389d1ab87 /tools/perf/scripts/python/Perf-Trace-Util/lib/Perf/Trace/Util.py
parent46af29e479cc0c1c63633007993af5292c2c3e75 (diff)
locking/mutexes: Modify the way optimistic spinners are queued
The mutex->spin_mlock was introduced in order to ensure that only 1 thread spins for lock acquisition at a time to reduce cache line contention. When lock->owner is NULL and the lock->count is still not 1, the spinner(s) will continually release and obtain the lock->spin_mlock. This can generate quite a bit of overhead/contention, and also might just delay the spinner from getting the lock. This patch modifies the way optimistic spinners are queued by queuing before entering the optimistic spinning loop as oppose to acquiring before every call to mutex_spin_on_owner(). So in situations where the spinner requires a few extra spins before obtaining the lock, then there will only be 1 spinner trying to get the lock and it will avoid the overhead from unnecessarily unlocking and locking the spin_mlock. Signed-off-by: Jason Low <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Signed-off-by: Peter Zijlstra <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]>
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