linux-kernel - Re: [PATCH] block: fix q->max_segment_size checking in blk_recalc_rq

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Date:	Thu, 24 Jul 2008 11:28:34 -0400
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	David Miller <davem@...emloft.net>, fujita.tomonori@....ntt.co.jp,
	jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-parisc@...r.kernel.org
Subject: Re: [PATCH] block: fix q->max_segment_size checking in
	blk_recalc_rq_segments about VMERGE

On Thu, 2008-07-24 at 11:07 -0400, Mikulas Patocka wrote:
> So try to #define BIO_VMERGE_BOUNDARY 0 for Pa-Risc and tell us what 
> performance degradation do you see (and what driver do you use and what is 
> the I/O pattern).
> 
> If you show something specific, we can consider that --- but you haven't 
> yet told us anything, except generic talk.

You keep ignoring inconvenient facts.  For about the third time:

I run a test bed for sg_tables (large chaining of requests).  This runs
on parisc using virtual merging (has to because the final physical table
size can't go over the sg list of the SCSI card).  If I turn off virtual
merging I can no longer test sg_tables in vanilla kernels.

James


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