From: James Bottomley <James.Bottomley@SteelEye.com>
To: Grant Grundler <grundler@parisc-linux.org>
Cc: parisc-linux@parisc-linux.org
Subject: Re: [parisc-linux] coherent ops and mb() revisited
Date: 04 Sep 2004 22:56:30 -0400 [thread overview]
Message-ID: <1094352991.1924.12.camel@mulgrave> (raw)
In-Reply-To: <20040905013844.GC23842@colo.lackof.org>
On Sat, 2004-09-04 at 21:38, Grant Grundler wrote:
> I haven't tested the following patch and just wanted to get
> feedback if it is "the right thing" or not.
It should work, but I don't think it's the right thing to do.
__ldcw already insists on operating on volatile data, which is the
correct thing to do. Adding a memory barrier is probably harmless, but
it crimps any optimisations gcc might like to try with that function
(not that there really are any with such a simple loop). Indeed, we
could even remove the __volatile__ from the asm.
I think the best implementation is probably
barrier();
a = __ldcw_align(x);
while (__ldcw(a) == 0)
while(*a == 0)
;
mb();
Which makes it totally clear what barriers we need where in the spinlock
(the first being simply a compiler ordering barrier and the second
actually a processor memory barrier).
James
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next prev parent reply other threads:[~2004-09-05 2:56 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-09-05 1:38 [parisc-linux] coherent ops and mb() revisited Grant Grundler
2004-09-05 2:56 ` James Bottomley [this message]
2004-09-05 6:27 ` John David Anglin
2004-09-05 14:36 ` James Bottomley
2004-09-06 4:19 ` Grant Grundler
2004-09-06 9:24 ` John David Anglin
2004-09-06 14:15 ` James Bottomley
2004-09-07 15:17 ` Grant Grundler
2004-09-07 15:30 ` James Bottomley
2004-09-08 16:52 ` Grant Grundler
2004-09-08 17:11 ` James Bottomley
2004-09-10 16:11 ` Grant Grundler
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