[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen: add persistent grants to xbd_xenbus
On Sun, Nov 04, 2012 at 11:23:50PM +0100, Roger Pau Monne wrote: > This patch implements persistent grants for xbd_xenbus (blkfront in > Linux terminology). 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. > > On startup xbd_xenbus notifies the backend driver that it is using > persistent grants. If the backend driver is not capable of persistent > mapping, xbd_xenbus will still use the same grants, since it is > compatible with the previous protocol, and simplifies the code > complexity in xbd_xenbus. > > Each time a request is send to the backend driver, xbd_xenbus will > check if there are free grants already mapped and will try to use one > of those. If there are not enough grants already mapped, xbd_xenbus > will request new grants, and they will be added to the list of free > grants when the transaction is finished, so they can be reused. Data > has to be copied from the request (struct buf) to the mapped grant, or > from the mapped grant to the request, depending on the operation being > performed. > > To test the performance impact of this patch I've benchmarked the > number of IOPS performed simultaneously by 15 NetBSD DomU guests on a > Linux Dom0 that supports persistent grants. The backend used to > perform this tests was a ramdisk of size 1GB. > > Sum of IOPS > Non-persistent 336718 > Persistent 686010 > > As seen, there's a x2 increase in the total number of IOPS being > performed. As a reference, using exactly the same setup Linux DomUs > are able to achieve 1102019 IOPS, so there's still plenty of room for > improvement. I'd like to see a similar test run against a NetBSD dom0. Also, how big are your IOPs ? -- Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx> NetBSD: 26 ans d'experience feront toujours la difference -- _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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