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

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Date:	Tue, 16 Dec 2014 11:32:31 +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>
Subject: Re: [Xen-devel] [PATCH] xen/blkfront: increase the default value
 of xen_blkif_max_segments

El 16/12/14 a les 11.11, Bob Liu ha escrit:
> The default maximum value of segments in indirect requests was 32, IO
> operations with bigger block size(>32*4k) would be split and performance start
> to drop.
> 
> Nowadays backend device usually support 512k max_sectors_kb on desktop, and
> may larger on server machines with high-end storage system.
> The default size 128k was not very appropriate, this patch increases the default
> maximum value to 128(128*4k=512k).

This looks fine, do you have any data/graphs to backup your reasoning?

I would also add to the commit message that 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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