On Tue, Jul 17, 2012 at 9:29 AM, Asias He <asias@xxxxxxxxxx> wrote: > On 07/16/2012 07:58 PM, Stefan Hajnoczi wrote: >> Does the vhost-blk implementation do anything fundamentally different >> from userspace? Where is the overhead that userspace virtio-blk has? > > > > Currently, no. But we could play with bio directly in vhost-blk as Christoph > suggested which could make the IO path from guest to host's real storage > even shorter in vhost-blk. Wait :). My point is that writing new code without systematically investigating performance means that we're essentially throwing random things and seeing what sticks. Adding bio mode would make vhost-blk and kvmtool more different. It'll probably make vhost-blk slightly faster but harder to compare against kvmtool. It's easier to start profiling before making that change. The reason I said "special-purpose kernel module" is because kvmtool could be suffering from a bottleneck that can be fixed. Other userspace applications would also benefit from that fix - it would be generally useful. Adding a vhost-blk kernel module works around this but only benefits KVM specifically. Stefan -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
