From: Oleg Nesterov <oleg@redhat.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ming Lei <tom.leiming@gmail.com>, Shaohua Li <shli@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org
Subject: Re: + atomic-improve-atomic_inc_unless_negative-atomic_dec_unless_positive .patch added to -mm tree
Date: Thu, 21 Mar 2013 19:30:21 +0100 [thread overview]
Message-ID: <20130321183021.GA27586@redhat.com> (raw)
In-Reply-To: <1363889025.4431.35.camel@edumazet-glaptop>
On 03/21, Eric Dumazet wrote:
>
> On Thu, 2013-03-21 at 18:08 +0100, Oleg Nesterov wrote:
>
> > OK... since nobody volunteered to make a patch, what do you think about
> > the change below?
> >
> > It should "fix" atomic_add_unless() (only on x86) and optimize
> > atomic_inc/dec_unless.
> >
> > With this change atomic_*_unless() can do the unnecessary mb() after
> > cmpxchg() fails, but I think this case is very unlikely.
> >
> > And, in the likely case atomic_inc/dec_unless avoids the 1st cmpxchg()
> > which in most cases just reads the memory for the next cmpxchg().
> >
> > Oleg.
>
> Hmm, cmpxchg() has different effect on MESI transaction, than a plain
> read.
But this doesn't matter?
We will do cmpxchg() anyway. Unless we can see that it will fail.
Or could you explain what I missed?
> maybe the 'hint' idea used in atomic_inc_not_zero_hint() could be used.
To me, it would be better to kill atomic_inc_not_zero_hint() or unify
unify it with atomic_inc_not_zero(). But this is another story.
Oleg.
next prev parent reply other threads:[~2013-03-21 18:32 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-14 16:24 + atomic-improve-atomic_inc_unless_negative-atomic_dec_unless_positive .patch added to -mm tree Oleg Nesterov
2013-03-15 3:46 ` Ming Lei
2013-03-15 13:46 ` Oleg Nesterov
2013-03-15 15:13 ` Ming Lei
2013-03-15 16:51 ` Oleg Nesterov
2013-03-15 17:23 ` Frederic Weisbecker
2013-03-15 17:51 ` Oleg Nesterov
2013-03-15 18:34 ` Frederic Weisbecker
2013-03-15 20:17 ` Paul E. McKenney
2013-03-16 18:30 ` Oleg Nesterov
2013-03-17 17:26 ` Paul E. McKenney
2013-03-21 17:08 ` Oleg Nesterov
2013-03-21 17:34 ` Paul E. McKenney
2013-03-21 18:03 ` Eric Dumazet
2013-03-21 18:30 ` Oleg Nesterov [this message]
2013-03-21 22:56 ` Eric Dumazet
2013-03-22 12:59 ` Oleg Nesterov
2013-03-22 16:34 ` Paul E. McKenney
2013-03-16 18:19 ` Oleg Nesterov
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