Messages in this thread | | | Date | Wed, 1 Feb 2006 02:49:13 -0800 | From | Jeremy Higdon <> | Subject | Re: [patch] SGIIOC4 limit request size |
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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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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