From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Linus Torvalds <torvalds@osdl.org>
Cc: David Howells <dhowells@redhat.com>,
Paul Mackerras <paulus@samba.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
akpm@osdl.org, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org, mingo@redhat.com, alan@redhat.com,
linuxppc64-dev@ozlabs.org
Subject: Re: [PATCH] Document Linux's memory barriers [try #4]
Date: Wed, 15 Mar 2006 12:25:13 +1100 [thread overview]
Message-ID: <44176CF9.90909@yahoo.com.au> (raw)
In-Reply-To: <Pine.LNX.4.64.0603141609520.3618@g5.osdl.org>
Linus Torvalds wrote:
>
>On Tue, 14 Mar 2006, David Howells wrote:
>
>>But that doesn't make any sense!
>>
>>That would mean we that we'd've read b into d before having read the new value
>>of p into q, and thus before having calculated the address from which to read d
>>(ie: &b) - so how could we know we were supposed to read d from b and not from
>>a without first having read p?
>>
>>Unless, of course, the smp_wmb() isn't effective, and the write to b happens
>>after the write to p; or the Alpha's cache isn't fully coherent.
>>
>
>The cache is fully coherent, but the coherency isn't _ordered_.
>
>
This is what I was referring to when I said your (David's) idea of "memory"
WRT memory consistency isn't correct -- cache coherency can be out of order.
--
Send instant messages to your online friends http://au.messenger.yahoo.com
next prev parent reply other threads:[~2006-03-15 1:25 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20060315200956.4a9e2cb3.akpm@osdl.org>
2006-03-09 20:29 ` [PATCH] Document Linux's memory barriers [try #4] David Howells
2006-03-09 23:34 ` Paul Mackerras
2006-03-09 23:45 ` Michael Buesch
2006-03-09 23:56 ` Linus Torvalds
2006-03-10 0:07 ` Michael Buesch
2006-03-10 0:48 ` Alan Cox
2006-03-10 0:54 ` Paul Mackerras
2006-03-10 15:19 ` David Howells
2006-03-11 0:01 ` Paul Mackerras
2006-03-10 5:28 ` Nick Piggin
2006-03-15 11:10 ` David Howells
2006-03-15 11:51 ` Nick Piggin
2006-03-15 13:47 ` David Howells
2006-03-15 23:21 ` Nick Piggin
2006-03-12 17:15 ` Eric W. Biederman
2006-03-14 21:26 ` David Howells
2006-03-14 21:48 ` Paul Mackerras
2006-03-14 23:59 ` David Howells
2006-03-15 0:20 ` Linus Torvalds
2006-03-15 1:19 ` David Howells
2006-03-15 1:47 ` Linus Torvalds
2006-03-15 1:25 ` Nick Piggin [this message]
2006-03-15 0:54 ` Paul Mackerras
2006-03-15 14:23 ` [PATCH] Document Linux's memory barriers [try #5] David Howells
2006-03-16 23:17 ` Paul E. McKenney
2006-03-16 23:55 ` Linus Torvalds
2006-03-17 1:29 ` Paul E. McKenney
2006-03-17 5:32 ` Linus Torvalds
2006-03-17 6:23 ` Paul E. McKenney
2006-03-23 18:34 ` David Howells
2006-03-23 19:28 ` Linus Torvalds
2006-03-23 22:26 ` Paul E. McKenney
[not found] ` <21253.1142509812@warthog.cambridge.redhat.com>
[not found] ` <Pine.LNX.4.64.0603160914410.3618@g5.osdl.org>
2006-03-17 1:20 ` Nick Piggin
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