Messages in this thread | | | Subject | Re: Announce: Semaphore-Removal tree | From | Peter Zijlstra <> | Date | Sat, 26 Apr 2008 15:39:13 +0200 |
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On Sat, 2008-04-26 at 05:30 -0400, Christoph Hellwig wrote: > On Fri, Apr 25, 2008 at 02:22:31PM -0700, Daniel Walker wrote: > > If you can make a case for converting some semaphores to spinlocks be my > > guest .. If you have good reasoning I wouldn't stand in the way.. (Real > > time converts all the spinlocks to mutexes anyway ..) > > Right at hand I have the XFS inode hash lock was converted from a rw_semaphore > to a rwlock_t becuase the context switch overhead was killing > performance in various benchmarks. This is a very typical scenary for > locks that are taken often and held for a rather short time. Add to > that fact that a spinlock is compltely optimized away for an UP kernel > while a mutex is not and the amount of memory that any mutex takes > compared to a spinlock you have a clear winner.
I'm guessing RCU would be a bit more work?
The problem with rwlock_t is that for it to be a spinning lock the hold times should be short, for it to be a rwlock over a spinlock there should be a significant amount of concurrency, these two things together make for a cache-line bouncing fest.
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