Michael S. Tsirkin wrote: > On Mon, Mar 22, 2010 at 05:34:04PM -0700, Badari Pulavarty wrote: > >> Write Results: >> ============== >> >> I see degraded IO performance when doing sequential IO write >> tests with vhost-blk compared to virtio-blk. >> >> # time dd of=/dev/vda if=/dev/zero bs=2M oflag=direct >> >> I get ~110MB/sec with virtio-blk, but I get only ~60MB/sec with >> vhost-blk. Wondering why ? >> > > Try to look and number of interrupts and/or number of exits. > I checked interrupts and IO exits - there is no major noticeable difference between vhost-blk and virtio-blk scenerios. > It could also be that you are overrunning some queue. > > I don't see any exit mitigation strategy in your patch: > when there are already lots of requests in a queue, it's usually > a good idea to disable notifications and poll the > queue as requests complete. That could help performance. > Do you mean poll eventfd for new requests instead of waiting for new notifications ? Where do you do that in vhost-net code ? Unlike network socket, since we are dealing with a file, there is no ->poll support for it. So I can't poll for the data. And also, Issue I am having is on the write() side. I looked at it some more - I see 512K write requests on the virtio-queue in both vhost-blk and virtio-blk cases. Both qemu or vhost is doing synchronous writes to page cache (there is no write batching in qemu that is affecting this case). I still puzzled on why virtio-blk outperforms vhost-blk. Thanks, Badari _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
