(xen) stable/for-jens-3.8

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!

 drivers/block/xen-blkback/blkback.c |  295 ++++++++++++++++++++++++++++++++---
 drivers/block/xen-blkback/common.h  |   17 ++
 drivers/block/xen-blkback/xenbus.c  |   23 +++-
 drivers/block/xen-blkfront.c        |  198 ++++++++++++++++++++----
 4 files changed, 478 insertions(+), 55 deletions(-)

Roger Pau Monne (2):
xen/blkback: Persistent grant maps for xen blk drivers xen/blkback: persistent-grants fixes

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

Jens Axboe