Messages in this thread | | | Date | Mon, 04 Aug 2014 11:44:19 -0400 | From | Waiman Long <> | Subject | Re: [PATCH 2/7] locking/rwsem: more aggressive use of optimistic spinning |
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On 08/04/2014 12:10 AM, Jason Low wrote: > On Sun, 2014-08-03 at 22:36 -0400, Waiman Long wrote: >> The rwsem_can_spin_on_owner() function currently allows optimistic >> spinning only if the owner field is defined and is running. That is >> too conservative as it will cause some tasks to miss the opportunity >> of doing spinning in case the owner hasn't been able to set the owner >> field in time or the lock has just become available. >> >> This patch enables more aggressive use of optimistic spinning by >> assuming that the lock is spinnable unless proved otherwise. >> >> Signed-off-by: Waiman Long<Waiman.Long@hp.com> >> --- >> kernel/locking/rwsem-xadd.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c >> index d058946..dce22b8 100644 >> --- a/kernel/locking/rwsem-xadd.c >> +++ b/kernel/locking/rwsem-xadd.c >> @@ -285,7 +285,7 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem) >> static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) >> { >> struct task_struct *owner; >> - bool on_cpu = false; >> + bool on_cpu = true; /* Assume spinnable unless proved not to be */ > Hi, > > So "on_cpu = true" was recently converted to "on_cpu = false" in order > to address issues such as a 5x performance regression in the xfs_repair > workload that was caused by the original rwsem optimistic spinning code. > > However, patch 4 in this patchset does address some of the problems with > spinning when there are readers. CC'ing Dave Chinner, who did the > testing with the xfs_repair workload. >
This patch set enables proper reader spinning and so the problem that we see with xfs_repair workload should go away. I should have this patch after patch 4 to make it less confusing. BTW, patch 3 can significantly reduce spinlock contention in rwsem. So I believe the xfs_repair workload should run faster with this patch than both 3.15 and 3.16.
-Longman
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