From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Hajnoczi Subject: Re: [PATCH 0/5] Add vhost-blk support Date: Mon, 16 Jul 2012 12:58:21 +0100 Message-ID: References: <1342107302-28116-1-git-send-email-asias@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: linux-kernel@vger.kernel.org, linux-aio@kvack.org, kvm@vger.kernel.org, "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, Benjamin LaHaise , Alexander Viro , linux-fsdevel@vger.kernel.org To: Asias He Return-path: In-Reply-To: <1342107302-28116-1-git-send-email-asias@redhat.com> Sender: owner-linux-aio@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Jul 12, 2012 at 4:35 PM, Asias He wrote: > This patchset adds vhost-blk support. vhost-blk is a in kernel virito-blk > device accelerator. Compared to userspace virtio-blk implementation, vhost-blk > gives about 5% to 15% performance improvement. Why is it 5-15% faster? vhost-blk and the userspace virtio-blk you benchmarked should be doing basically the same thing: 1. An eventfd file descriptor is signalled when the vring has new requests available from the guest. 2. A thread wakes up and processes the virtqueue. 3. Linux AIO is used to issue host I/O. 4. An interrupt is injected into the guest. Does the vhost-blk implementation do anything fundamentally different from userspace? Where is the overhead that userspace virtio-blk has? I'm asking because it would be beneficial to fix the overhead (especially it that could speed up all userspace applications) instead of adding a special-purpose kernel module to work around the overhead. Stefan -- To unsubscribe, send a message with 'unsubscribe linux-aio' in the body to majordomo@kvack.org. For more info on Linux AIO, see: http://www.kvack.org/aio/ Don't email: aart@kvack.org