From: Jens Axboe <jens.axboe@oracle.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Alasdair G Kergon <agk@redhat.com>,
dm-devel@redhat.com, linux-kernel@vger.kernel.org,
Heinz Mauelshagen <hjm@redhat.com>
Subject: Re: [2.6.22 PATCH 22/26] dm: bio list helpers
Date: Wed, 9 May 2007 08:49:23 +0200 [thread overview]
Message-ID: <20070509064923.GO4163@kernel.dk> (raw)
In-Reply-To: <20070508174159.7d78a275.akpm@linux-foundation.org>
On Tue, May 08 2007, Andrew Morton wrote:
> > static inline void bio_list_init(struct bio_list *bl)
> > {
> > bl->head = bl->tail = NULL;
> > }
> >
> > +#define bio_list_for_each(bio, bl) \
> > + for (bio = (bl)->head; bio && ({ prefetch(bio->bi_next); 1; }); \
> > + bio = bio->bi_next)
> > +
>
> I have this vague memory from a long time ago that one particular CPU type
> wants to go oops when prefetching from an invalid address.
>
> Maybe that went away for some reason - we'd have hit it again if it was
> real.
Besides, manual prefetching is very rarely a win. I dabbled with some
benchmarks a few weeks back (with the doubly linked lists), and in most
cases it was actually a loss. So I'd vote for just removing the
prefetch() above.
--
Jens Axboe
next prev parent reply other threads:[~2007-05-09 6:52 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-08 19:48 [2.6.22 PATCH 22/26] dm: bio list helpers Alasdair G Kergon
2007-05-09 0:41 ` Andrew Morton
2007-05-09 6:49 ` Jens Axboe [this message]
2007-05-09 15:54 ` Alasdair G Kergon
2007-05-10 14:17 ` Jan Engelhardt
2007-05-10 14:29 ` Alan Cox
2007-05-10 21:40 ` Jens Axboe
2007-05-09 15:47 ` Alasdair G Kergon
2007-05-10 13:41 ` Andi Kleen
2007-05-10 14:17 ` Jan Engelhardt
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