From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Roland Dreier <rdreier@cisco.com>
Cc: Jes Sorensen <jes@sgi.com>,
"Bryan O'Sullivan" <bos@pathscale.com>,
Andrew Morton <akpm@osdl.org>, Andi Kleen <ak@suse.de>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Define wc_wmb, a write barrier for PCI write combining
Date: Tue, 28 Feb 2006 09:13:41 -0800 [thread overview]
Message-ID: <200602280913.41938.jbarnes@virtuousgeek.org> (raw)
In-Reply-To: <adafym3l8lk.fsf@cisco.com>
On Tuesday, February 28, 2006 9:02 am, Roland Dreier wrote:
> Jes> Not quite correct as far as I understand it. mmiowb() is
> Jes> supposed to guarantee that writes to MMIO space have
> Jes> completed before continuing. That of course covers the
> Jes> multi-CPU case, but it should also cover the write-combining
> Jes> case.
>
> I don't believe this is correct. mmiowb() does not guarantee that
> writes have completed -- they may still be pending in a buffer in a
> bridge somewhere. The _only_ effect of mmiowb() is to make sure that
> writes which have been ordered between CPUs using some other mechanism
> (i.e. a lock) are properly ordered by the rest of the system. This
> only has an effect systems like very large ia64 systems, where (as I
> understand it), writes can pass each other on the way to the PCI bus.
> In fact, mmiowb() is a NOP on essentially every architecture.
I think it could be implemented meaningfully on ppc64, mips64, and
perhaps some parisc systems, but I don't think their respective
maintainers have gotten around to that yet.
Anyway, it looks like the write combine ordering Bryan is talking about
really is a distinct semantic. Not sure if it's possible (or desirable)
to overload an existing barrier op to include the semantics he wants.
Jesse
next prev parent reply other threads:[~2006-02-28 17:13 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-25 4:20 [PATCH] Define wc_wmb, a write barrier for PCI write combining Bryan O'Sullivan
2006-02-25 4:43 ` Andi Kleen
2006-02-25 7:34 ` Bryan O'Sullivan
2006-02-25 13:28 ` Andi Kleen
2006-02-25 17:20 ` Bryan O'Sullivan
2006-02-25 19:01 ` Bryan O'Sullivan
2006-02-28 17:44 ` Jesse Barnes
2006-02-28 17:50 ` Roland Dreier
2006-02-28 17:50 ` Jesse Barnes
2006-02-28 17:52 ` Bryan O'Sullivan
2006-02-28 17:59 ` Jesse Barnes
2006-02-25 14:28 ` Benjamin LaHaise
2006-02-25 17:11 ` Bryan O'Sullivan
2006-02-25 17:41 ` Benjamin LaHaise
2006-02-28 17:50 ` Bryan O'Sullivan
2006-02-28 17:58 ` Benjamin LaHaise
2006-02-28 18:20 ` Bryan O'Sullivan
2006-02-28 19:03 ` Benjamin LaHaise
2006-02-28 19:20 ` Bryan O'Sullivan
2006-02-28 19:33 ` Andi Kleen
2006-02-28 19:44 ` Bryan O'Sullivan
2006-03-01 19:20 ` Bryan O'Sullivan
2006-03-01 19:27 ` Andi Kleen
2006-03-01 19:43 ` Bryan O'Sullivan
2006-03-01 19:49 ` Andi Kleen
2006-03-01 20:05 ` Bryan O'Sullivan
2006-03-01 20:26 ` Benjamin LaHaise
2006-03-01 20:35 ` Bryan O'Sullivan
2006-02-28 19:34 ` Benjamin LaHaise
2006-02-28 18:22 ` Christopher Friesen
2006-02-28 10:01 ` Jes Sorensen
2006-02-28 15:42 ` Roland Dreier
2006-02-28 16:08 ` Jes Sorensen
2006-02-28 17:02 ` Roland Dreier
2006-02-28 17:13 ` Jesse Barnes [this message]
2006-02-28 17:20 ` Jes Sorensen
2006-03-01 8:16 ` Jeremy Higdon
2006-03-01 8:24 ` Jeremy Higdon
2006-02-28 17:11 ` Jesse Barnes
2006-02-28 17:57 ` Bryan O'Sullivan
2006-02-28 18:07 ` linux-os (Dick Johnson)
2006-02-28 18:24 ` Christopher Friesen
2006-03-01 10:45 ` Jes Sorensen
2006-03-01 17:04 ` Roland Dreier
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