Messages in this thread Patch in this message | | | Date | Wed, 1 Feb 2006 12:08:30 +0100 | From | Bartlomiej Zolnierkiewicz <> | Subject | Re: [patch] SGIIOC4 limit request size |
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On 2/1/06, Jeremy Higdon <jeremy@sgi.com> wrote: > 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
Indeed, seems that hwif->max_sg_nents is not respected when setting queue ->max_hw_segments and ->max_phys_segments.
Does the logic really work the same? Isn't PCI_DMA_BUS_IS_PHYS == 0 for SN2?
If so then the code sets ->max_{hw,phys}_segments to IOC4_PRD_ENTRIES/2 which actually shouldn't hurt...
> 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.
I have no big problem with applying patch as it is but I think that it just hides the real problem and/or makes it harder to hit...
Bartlomiej
> 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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