Groups > linux.kernel > #1199236

Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel locking

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel locking
Date	2015-08-03 22:10 +0200
Message-ID	<pTudA-4Zd-15@gated-at.bofh.it> (permalink)
References	(2 earlier) <pNnot-3xc-3@gated-at.bofh.it> <pRXjI-1kU-7@gated-at.bofh.it> <pRY67-2v3-35@gated-at.bofh.it> <pRYfL-2Gd-11@gated-at.bofh.it> <pTudz-4Zd-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Aug 03, 2015 at 04:05:33PM -0400, Steven Rostedt wrote:
> On Thu, 30 Jul 2015 17:40:01 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Thu, Jul 30, 2015 at 08:34:52AM -0700, Paul E. McKenney wrote:
> > > > If the extra read before the cmpxchg() does not hurt, we should do the
> > > > same for mutex and make the above redundant.
> > > 
> > > I am pretty sure that different hardware wants it done differently.  :-/
> > > So I agree that hard data would be good.
> > > 
> > > I could probably further optimize the RCU code by checking for a
> > > single-node tree, but I am not convinced that this is worthwhile.
> > > However, skipping three cache misses in the uncontended case is
> > > definitely worthwhile, hence this patch.  ;-)
> > 
> > I was mostly talking about the !mutex_is_locked() && mutex_try_lock()
> > thing. The fast path thing makes sense.
> 
> Note, mutex does do this for the optimistic spin. See
> mutex_try_to_aquire().

Right but that's mutex_lock(). mutex_trylock() does not.
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Thread

Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel  locking Peter Zijlstra <peterz@infradead.org> - 2015-07-30 16:50 +0200
  Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel  locking "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-30 17:40 +0200
    Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel  locking Peter Zijlstra <peterz@infradead.org> - 2015-07-30 17:50 +0200
      Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel  locking Steven Rostedt <rostedt@goodmis.org> - 2015-08-03 22:10 +0200
        Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel  locking Peter Zijlstra <peterz@infradead.org> - 2015-08-03 22:10 +0200
    Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel  locking "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-31 18:00 +0200

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