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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

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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