linux-kernel - Re: [GIT PULL] (xen) stable/for-jens-3.8

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Date:	Mon, 12 Nov 2012 09:19:14 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com
Subject: Re: [GIT PULL] (xen) stable/for-jens-3.8

On 2012-11-09 07:55, Konrad Rzeszutek Wilk wrote:
> Hey Jens,
> 
> Please git pull the following branch:
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git stable/for-jens-3.8
> 
> which has a new feature of the blk[back|front] driver - it is called 'feature-persistent'.
> Roger and Oliver patch says:
> "  This patch implements persistent grants for the xen-blk{front,back}
>     mechanism. The effect of this change is to reduce the number of unmap
>     operations performed, since they cause a (costly) TLB shootdown. This
>     allows the I/O performance to scale better when a large number of VMs
>     are performing I/O.
>     
>     Previously, the blkfront driver was supplied a bvec[] from the request
>     queue. This was granted to dom0; dom0 performed the I/O and wrote
>     directly into the grant-mapped memory and unmapped it; blkfront then
>     removed foreign access for that grant. The cost of unmapping scales
>     badly with the number of CPUs in Dom0. An experiment showed that when
>     Dom0 has 24 VCPUs, and guests are performing parallel I/O to a
>     ramdisk, the IPIs from performing unmap's is a bottleneck at 5 guests
>     (at which point 650,000 IOPS are being performed in total). If more
>     than 5 guests are used, the performance declines. By 10 guests, only
>     400,000 IOPS are being performed.
>     
>     This patch improves performance by only unmapping when the connection
>     between blkfront and back is broken.
> "
> 
> Note: You might get a conflict in the common.h file. It should
> be fairly easy to fix it - it should end up looking as this:
> 
> 160         /* Cached size parameter. */
> 161         sector_t                size;
> 162         unsigned int            flush_support:1;
> 163         unsigned int            discard_secure:1;
> 164         unsigned int            feature_gnt_persistent:1;
> 165         unsigned int            overflow_max_grants:1;
> 166 };
> 
> Thanks!

Thanks, pulled. No conflict observed, it merged cleanly.

-- 
Jens Axboe

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