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From: Grant Grundler <iod00d@hp.com>
To: linux-ia64@vger.kernel.org
Subject: Re: SCSI ERRORS triggered by BIO_VMERGE_BOUNDARY
Date: Tue, 24 Jun 2003 21:07:17 +0000	[thread overview]
Message-ID: <marc-linux-ia64-105648893606349@msgid-missing> (raw)
In-Reply-To: <marc-linux-ia64-105604433402604@msgid-missing>

On Mon, Jun 23, 2003 at 03:05:49PM -0700, Grant Grundler wrote:
> It looks like blk_recount_segments() is only used to gather
> stastics about how many segments are in the transaction.
> I tracked back to fs/bio.c to find the consumer of this
> information (# of segments) but didn't find it.
> Anyone know off hand?

James Bottomley explained it to me:

| The second is this nr_phys_segments in the elevator queuing code.  This   
| counts the number of SG entries that will be required to describe the
| request.  A lot of devices have fixed size SG tables, so the SG table is
| the only thing that limits the size of the transfer.  Thus the block
| layer has code that tries to merge physically contiguous segments of a
| bio so it can squeeze extra blocks into the transfer.

I don't know if LSI SCSI controllers/drivers have limits in this space
and what they might be. Will try to figure that out.

thanks,
grant

      parent reply	other threads:[~2003-06-24 21:07 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-06-19 17:36 SCSI ERRORS triggered by BIO_VMERGE_BOUNDARY David Mosberger
2003-06-19 20:48 ` Jesse Barnes
2003-06-19 21:47 ` Grant Grundler
2003-06-23  7:11 ` Grant Grundler
2003-06-23 15:04 ` Alex Williamson
2003-06-23 16:52 ` David Mosberger
2003-06-23 20:24 ` Grant Grundler
2003-06-23 20:41 ` David Mosberger
2003-06-23 22:05 ` Grant Grundler
2003-06-23 22:14 ` David Mosberger
2003-06-24 21:07 ` Grant Grundler [this message]

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