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SubjectRe: [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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