From: Jens Axboe <jens.axboe@oracle.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: dm-devel@redhat.com, Heinz Mauelshagen <hjm@redhat.com>,
linux-kernel@vger.kernel.org, Alasdair G Kergon <agk@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
WARNING: multiple messages have this Message-ID (diff)
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 6:49 UTC|newest]
Thread overview: 14+ 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 6:49 ` Jens Axboe
2007-05-09 15:54 ` Alasdair G Kergon
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 14:29 ` Alan Cox
2007-05-10 21:40 ` Jens Axboe
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20070509064923.GO4163@kernel.dk \
--to=jens.axboe@oracle.com \
--cc=agk@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=dm-devel@redhat.com \
--cc=hjm@redhat.com \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.