Subject: Re: New device buffer queue strategy
To: None <email@example.com>
From: Bang Jun-Young <firstname.lastname@example.org>
Date: 09/03/2002 13:29:23
On Tue, Sep 03, 2002 at 10:37:21AM +0900, Bang Jun-Young wrote:
> On Mon, Sep 02, 2002 at 04:05:40PM +0200, Juergen Hannken-Illjes wrote:
> > A new device buffer queue strategy is available for testing.
> > The current implementation of disksort (a min seek sort) doesn't perform
> > very well with long queues of outstanding requests. Especially with
> > softdeps this is a very common situation. As all requests are ordered the
> > read latency may become very high.
> > The new strategy keeps disksort for write-requests while read-requests are
> > put on a second queue with first-come first-serve strategy.
> > Read-requests are served before write-requests.
> > While the overall I/O performance is the same, the system becomes more
> > responsive under high I/O load.
> > To test this strategy:
> > - lookup the `bufq_alloc' call in your favorite disk driver:
> > ! sys/dev/scsipi/sd.c: bufq_alloc(&sd->buf_queue, BUFQ_DISKSORT|BUFQ_SORT_RAWBLOCK);
> > - replace the BUFQ_DISKSORT argument by BUFQ_READ_PRIO.
> > ! sys/dev/scsipi/sd.c: bufq_alloc(&sd->buf_queue, BUFQ_READ_PRIO|BUFQ_SORT_RAWBLOCK);
> > - recompile kernel and test.
> > Comments and improvements are welcome.
> After patching sys/dev/ata/wd.c as described above, my machine is much
> more responsive than before when I do 'cvs update'. Thanks!
Oops, the patch was very dangerous! One of my hard drives (softdep
enabled) got corrupted during reboot process. An error message was
displayed on the screen, but I couldn't read it.
Bang Jun-Young <email@example.com>