Messages in this thread | | | Date | Wed, 24 Aug 2016 17:54:32 +0100 | From | Will Deacon <> | Subject | Re: [RFC][PATCH 1/3] locking/mutex: Rework mutex::owner |
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On Wed, Aug 24, 2016 at 06:52:44PM +0200, Peter Zijlstra wrote: > On Wed, Aug 24, 2016 at 05:34:12PM +0200, Peter Zijlstra wrote: > > On Wed, Aug 24, 2016 at 10:56:59AM +0100, Will Deacon wrote: > > > > + owner = atomic_long_read(&lock->owner); > > > > + for (;;) { > > > > + unsigned long old; > > > > + > > > > + old = atomic_long_cmpxchg_release(&lock->owner, owner, owner & 0x03); > > > > + if (old == owner) > > > > + break; > > > > + > > > > + owner = old; > > > > + } > > > > > > Can you rewrite this using atomic_long_fetch_and_release? > > > > Yes, until patch 3/3.. but now that you mention it I think we can do: > > > > owner = atomic_long_read(&lock->owner); > > if (!(owner & MUTEX_FLAG_HANDOFF)) > > (void)atomic_long_fetch_and_release(MUTEX_FLAGS, &lock->owner); > > > > And of course, x86 would very much like atomic_long_and_release() here, > such that it can do LOCK ADD instead of a LOCK CMPXCHG loop. But of > course, we don't have that ...
... yeah, I noticed that. There is a curious use of atomic_and in linux/atomic.h, but it's packed full of false promises.
Will
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