From: Jeremy Higdon <jeremy@sgi.com>
To: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Cc: Jes Sorensen <jes@sgi.com>, Alan Cox <alan@redhat.com>,
Linus Torvalds <torvalds@osdl.org>,
linux-kernel@vger.kernel.org
Subject: Re: [patch] SGIIOC4 limit request size
Date: Wed, 1 Feb 2006 02:49:13 -0800 [thread overview]
Message-ID: <20060201104913.GA152005@sgi.com> (raw)
In-Reply-To: <58cb370e0602010234p62521a00h6d8920c84cac44d5@mail.gmail.com>
On Wed, Feb 01, 2006 at 11:34:18AM +0100, Bartlomiej Zolnierkiewicz wrote:
> On 01 Feb 2006 03:59:16 -0500, Jes Sorensen <jes@sgi.com> wrote:
> > Hi,
>
> Hi,
>
> > This one takes care of a problem with the SGI IOC4 driver where it
> > hits DMA problems if the request grows too large.
>
> Does this happen only for CONFIG_IA64_PAGE_SIZE_4KB=y
> or CONFIG_IA64_PAGE_SIZE_8KB=y?
Actually, it happens with a 16KB page size.
> from sgiioc4.c:
>
> /* Each Physical Region Descriptor Entry size is 16 bytes (2 * 64 bits) */
> /* IOC4 has only 1 IDE channel */
> #define IOC4_PRD_BYTES 16
> #define IOC4_PRD_ENTRIES (PAGE_SIZE /(4*IOC4_PRD_BYTES))
>
> As limiting request size to 127 sectors punishes performance
> wouldn't it be better to define IOC4_PRD_ENTRIES to 256
> if this is possible (would need 4 pages for PAGE_SIZE=4096
> and 2 for PAGE_SIZE=8192)?
I may be misunderstanding something, but it looks to me as though
IOC4_PRD_ENTRIES may be ignored, since ide_init_queue() just uses
PRD_ENTRIES. Fortunately, with a 16KB page size, the arithmetic
works out to the same. In any case, it seems that the 64KB
limit is the problem. Whether that is due to too many s/g entries
or total byte count I cannot say. I do know that with a 2KB
physical sector size, the minimum size for a s/g entry should be
2KB, which would mean we're using at most 32 with 127 max sectors --
well below the 256 that we get from PRD_ENTRIES and IOC4_PRD_ENTRIES.
We're still looking for root cause of this problem. But with the
default 128KB max request size, we occasionally get timeouts on
DMA commands.
jeremy
> Cheers.
> Bartlomiej
>
> > Cheers,
> > Jes
> >
> > Avoid requests larger than the number of SG table entries, to avoid
> > DMA timeouts.
> >
> > Signed-off-by: Jes Sorensen <jes@sgi.com>
> >
> > ----
> >
> > drivers/ide/pci/sgiioc4.c | 8 +++++++-
> > 1 files changed, 7 insertions(+), 1 deletion(-)
> >
> > Index: linux-2.6/drivers/ide/pci/sgiioc4.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/ide/pci/sgiioc4.c
> > +++ linux-2.6/drivers/ide/pci/sgiioc4.c
> > @@ -1,5 +1,5 @@
> > /*
> > - * Copyright (c) 2003 Silicon Graphics, Inc. All Rights Reserved.
> > + * Copyright (C) 2003, 2006 Silicon Graphics, Inc. All Rights Reserved.
> > *
> > * This program is free software; you can redistribute it and/or modify it
> > * under the terms of version 2 of the GNU General Public License
> > @@ -613,6 +613,12 @@
> > hwif->ide_dma_lostirq = &sgiioc4_ide_dma_lostirq;
> > hwif->ide_dma_timeout = &__ide_dma_timeout;
> > hwif->INB = &sgiioc4_INB;
> > +
> > + /*
> > + * Limit the request size to avoid DMA timeouts when
> > + * requesting more entries than goes in the sg table.
> > + */
> > + hwif->rqsize = 127;
> > }
> >
> > static int __devinit
next prev parent reply other threads:[~2006-02-01 10:49 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-01 8:59 [patch] SGIIOC4 limit request size Jes Sorensen
2006-02-01 10:34 ` Bartlomiej Zolnierkiewicz
2006-02-01 10:41 ` Jes Sorensen
2006-02-01 10:49 ` Jeremy Higdon [this message]
2006-02-01 11:08 ` Bartlomiej Zolnierkiewicz
2006-02-01 11:17 ` Jeremy Higdon
2006-02-01 11:26 ` Bartlomiej Zolnierkiewicz
2006-02-01 11:36 ` Jeremy Higdon
2006-02-01 12:44 ` Bartlomiej Zolnierkiewicz
2006-02-02 8:00 ` [patch] Fix DMA timeouts with sgiioc4 Jeremy Higdon
2006-02-02 8:45 ` Jes Sorensen
2006-02-01 13:39 ` [patch] SGIIOC4 limit request size Alan Cox
2006-02-01 14:53 ` Bartlomiej Zolnierkiewicz
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