From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>,
paulmck@linux.vnet.ibm.com, dhowells@redhat.com,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: memory barrier question
Date: Sat, 18 Sep 2010 07:49:08 +1000 [thread overview]
Message-ID: <1284760148.30449.107.camel@pasglop> (raw)
In-Reply-To: <E1OwI5H-0007LR-DC@pomaz-ex.szeredi.hu>
> Right but in the concrete namei example I can't see how a compiler
> optimization can make a difference. The order of the loads is quite
> clear:
>
> LOAD inode = next.dentry->inode
> if (inode != NULL)
> LOAD inode->f_op
>
> What is there the compiler can optimize?
Those two loads depend on each other, I don't think any implementation
can re-order them. In fact, such data dependency is typically what is
used to avoid having barriers in some cases. The second load cannot be
issued until the value from the first one is returned.
Cheers,
Ben.
next prev parent reply other threads:[~2010-09-17 21:49 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-15 14:36 memory barrier question Miklos Szeredi
2010-09-15 14:36 ` Miklos Szeredi
2010-09-15 19:12 ` Rafael J. Wysocki
2010-09-16 11:55 ` David Howells
2010-09-16 13:42 ` Miklos Szeredi
2010-09-16 13:42 ` Miklos Szeredi
2010-09-16 14:30 ` David Howells
2010-09-16 15:03 ` Paul E. McKenney
2010-09-16 15:03 ` Paul E. McKenney
2010-09-16 16:06 ` Miklos Szeredi
2010-09-16 16:06 ` Miklos Szeredi
2010-09-16 16:37 ` Paul E. McKenney
2010-09-16 16:56 ` Miklos Szeredi
2010-09-16 17:09 ` James Bottomley
2010-09-16 17:17 ` Miklos Szeredi
2010-09-16 17:40 ` James Bottomley
2010-09-17 21:49 ` Benjamin Herrenschmidt [this message]
2010-09-17 23:12 ` Paul E. McKenney
2010-09-19 2:47 ` Benjamin Herrenschmidt
2010-09-19 15:26 ` Paul E. McKenney
2010-09-19 20:15 ` Miklos Szeredi
2010-09-19 21:59 ` Paul E. McKenney
2010-09-20 0:58 ` James Bottomley
2010-09-20 1:29 ` Paul E. McKenney
2010-09-20 16:01 ` Miklos Szeredi
2010-09-20 18:25 ` Paul E. McKenney
2010-09-20 18:57 ` Paul E. McKenney
2010-09-20 20:26 ` Michael Cree
2010-09-20 20:40 ` Paul E. McKenney
2010-09-21 14:59 ` Paul E. McKenney
2010-09-22 18:41 ` Paul E. McKenney
2010-09-18 1:12 ` Alan Cox
2010-09-16 16:50 ` Jamie Lokier
2010-09-16 16:18 ` Peter Zijlstra
2010-09-16 17:59 ` David Howells
-- strict thread matches above, loose matches on Subject: below --
2010-09-20 10:34 George Spelvin
2010-09-20 10:34 ` George Spelvin
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