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From: David Miller <davem@davemloft.net>
To: john.dykstra1@gmail.com
Cc: netdev@vger.kernel.org, pcnet32@verizon.net
Subject: Re: [PATCH net-next-2.6] pcnet32: Remove pointless memory barriers
Date: Tue, 28 Apr 2009 22:16:05 -0700 (PDT)	[thread overview]
Message-ID: <20090428.221605.71993506.davem@davemloft.net> (raw)
In-Reply-To: <1240945659.8819.9.camel@Maple>

From: John Dykstra <john.dykstra1@gmail.com>
Date: Tue, 28 Apr 2009 19:07:39 +0000

> These two memory barriers in performance-critical paths are not needed
> on x86.  Even if some other architecture does buffer PCI I/O space
> writes, the existing memory-mapped I/O barriers are unlikely to be what
> is needed.
> 
> Signed-off-by: John Dykstra <john.dykstra1@gmail.com>

Any driver where these things are present usually has them
there for a reason.  Usually it's because the SGI guys really
did run into real problems without them on their huge
machines which can reorder PCI MMIO wrt. real memory operations.

I don't feel good applying this at all, given that I see no
evidence that there has been any investigation into how these
barriers got there in the first place.

  reply	other threads:[~2009-04-29  5:16 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-04-28 19:07 [PATCH net-next-2.6] pcnet32: Remove pointless memory barriers John Dykstra
2009-04-29  5:16 ` David Miller [this message]
2009-04-29 13:48   ` John Dykstra
2009-04-29 17:10     ` Don Fry
2009-04-29 19:07       ` John Dykstra
2009-04-29 22:29       ` Francois Romieu
2009-04-30  0:09 ` Don Fry
2009-04-30  0:16   ` John Dykstra
2009-04-30  0:21     ` David Miller
2009-04-30  0:19   ` David Miller

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