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
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