linux-kernel - Re: linux-next: Tree for July 16 (crash on quad core AMD)

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Message-ID: <20080719033050.552f9b49@mjolnir.drzeus.cx>
Date:	Sat, 19 Jul 2008 03:30:50 +0200
From:	Pierre Ossman <drzeus@...eus.cx>
To:	Tejun Heo <htejun@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	scsi <linux-scsi@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-ide <linux-ide@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>, Takashi Iwai <tiwai@...e.de>,
	tino.keitel@....de
Subject: Re: linux-next: Tree for July 16 (crash on quad core AMD)

On Sat, 19 Jul 2008 09:59:11 +0900
Tejun Heo <htejun@...il.com> wrote:

> Pierre Ossman wrote:
> > I just have one objection to your version, and that is that it cannot
> > be used to nibble away at the sg list. The _next() call jumps an entire
> > page, whereas you sometimes need to consume that page in two different
> > sweeps. This could be handled by some external buffer that keeps the
> > remainder of the page, but the point of these functions was to keep
> > things simple for the callers.
> 
> Well, I don't know how often such usages would be necessary.  If it's a
> very common ops, you can add a param to the next function but frankly I
> think it's better to build a inside control structure for that.  There's
> no need for external buffer, just an inner loop is sufficient.
> 

I'm not sure how this can be solved by an inner loop. My primary use
case is:

1. Wait for interrupt
2. Write n bytes
3. goto 1

n has no guarantee of being aligned to any page boundaries, so state
needs to be kept between each invokation of writing a chunk of data. I
doubt I'm alone in this use pattern (in fact, most device drivers using
PIO should do something similar).

-- 
     -- Pierre Ossman

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