netdev - Re: [PATCH net-next-2.6] pcnet32: Remove pointless memory barriers

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Message-ID: <20090429222906.GA16498@electric-eye.fr.zoreil.com>
Date:	Thu, 30 Apr 2009 00:29:06 +0200
From:	Francois Romieu <romieu@...zoreil.com>
To:	Don Fry <pcnet32@...izon.net>
Cc:	John Dykstra <john.dykstra1@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	jeff@...zik.org
Subject: Re: [PATCH net-next-2.6] pcnet32: Remove pointless memory barriers

Don Fry <pcnet32@...izon.net> :
> My original NAPI implementation did not have the mmiowb() but it was
> added because of some comments from Francois Romeiu (2006-06-29/30).  I
> do not know if they are required or not.  My feeling was/is that they
> are not as the writes are flushed with the unlocking primitives.
> However that is not based on knowledge, just "feeling".

(not sure if anyone should care about the loss of performance on x86
for a memory barrier near a couple of PCI I/O accesses but...)

I take back my comment from 2006 as I did not notice that there were
PCI I/O space accesses only.

-- 
Ueimor
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