linux-kernel - Re: bnx2 fails to compile on parisc because of missing get_dma

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Message-ID: <C27F8246C663564A84BB7AB3439772421B79CBCA21@IRVEXCHCCR01.corp.ad.broadcom.com>
Date:	Thu, 17 Jun 2010 06:30:39 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"'James Bottomley'" <JBottomley@...ell.com>
cc:	"'FUJITA Tomonori'" <fujita.tomonori@....ntt.co.jp>,
	"vapier@...too.org" <vapier@...too.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: bnx2 fails to compile on parisc because of missing
 get_dma_ops()

James Bottomley wrote:

> On Thu, 2010-06-17 at 05:54 -0700, Michael Chan wrote:
> > This prefetch improves performance noticeably when the driver is
> > handling incoming 64-byte packets at a sustained rate.
>
> So why not do it unconditionally?  The worst that can happen
> is that you
> pull in a stale cache line which will get cleaned in the
> dma_sync, thus
> slightly degrading performance on incoherent architectures.

The original patch was an unconditional prefetch.  There was
some discussion that it might not be correct if the DMA wasn't
sync'ed yet on some archs.  If the concensus is that it is ok to
do so, that would be the simplest solution.

>
> Alternatively, come up with a dma prefetch infrastructure ...
> all you're
> really doing is hinting to the architecture that you'll sync
> this region
> next.
>
> James
>
>
>
>

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