[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] Persistent grant maps for xen blk drivers
On Wed, Sep 19, 2012 at 11:51:27AM +0100, Oliver Chick wrote: > 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. > So how many IOPS can you get with this patch / persistent grants ? -- Pasi _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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