On Tue, Jul 17, 2012 at 12:42 PM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote: > On Tue, Jul 17, 2012 at 12:26 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: >> On Tue, Jul 17, 2012 at 12:11:15PM +0100, Stefan Hajnoczi wrote: >>> On Tue, Jul 17, 2012 at 10:21 AM, Asias He <asias@xxxxxxxxxx> wrote: >>> > On 07/17/2012 04:52 PM, Paolo Bonzini wrote: >>> >> >>> >> Il 17/07/2012 10:29, Asias He ha scritto: >>> >>> >>> >>> So, vhost-blk at least saves ~6 syscalls for us in each request. >>> >> >>> >> >>> >> Are they really 6? If I/O is coalesced by a factor of 3, for example >>> >> (i.e. each exit processes 3 requests), it's really 2 syscalls per request. >>> > >>> > >>> > Well. I am counting the number of syscalls in one notify and response >>> > process. Sure the IO can be coalesced. >>> >>> Linux AIO also supports batching in io_submit() and io_getevents(). >>> Depending on the request pattern in the vring when you process it, you >>> should be able to do better than 1 set of syscalls per host I/O >>> request. >>> >>> Are you taking advantage of that at the moment in your userspace benchmark? >>> >>> Stefan >> >> Injecting an interrupt directly from kernel bypasses two context switches. >> Yes some worloads can coalesce interrupts efficiently but others can't. >> It is not really hard to speculate more. >> >> Personally I don't understand where all this speculation leads us. >> Are you guys disputing the measurements posted? If not would not >> it be better if discussion focused on the amount of extra code versus >> measured gain? > > 5-15% is nice. But what causes the performance advantage? To be clear, I suggest posting profiling results and explaining the improvement over kvmtool. Stefan _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
