linux-kernel - Re: [RESEND PATCH] xen/blkfront: increase the default value of xen_blkif_max

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Date:	Wed, 21 Jan 2015 11:13:56 +0100
From:	Roger Pau Monné <roger.pau@...rix.com>
To:	Bob Liu <bob.liu@...cle.com>, <xen-devel@...ts.xen.org>
CC:	<david.vrabel@...rix.com>, <linux-kernel@...r.kernel.org>,
	<konrad.wilk@...cle.com>
Subject: Re: [RESEND PATCH] xen/blkfront: increase the default value of xen_blkif_max_segments

El 21/01/15 a les 8.56, Bob Liu ha escrit:
> The default max-segments of indirect requests was 32, so IO operations with
> bigger block size(>32*4k) would be split and make performance drop.
> 
> Nowadays backend device usually support 512k max_sectors_kb on desktop,
> and usually larger on server machines connected with high-end storage system.
> The default max size(128k) is not appropriate anymore, this patch increases it
> to 128(128*4k=512k).
> 
> Signed-off-by: Bob Liu <bob.liu@...cle.com>

Looks fine to me, the Linux backend is also prepared to handle it
without any modifications. As I said in the last version, I would add
the following to the commit message:

This change implies we can now have 32*128+32 = 4128 in-flight grants,
which greatly surpasses the default amount of persistent grants blkback
can handle, so the LRU in blkback will kick in.

Roger.
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