On Wed, Feb 9, 2011 at 1:55 AM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > On Wed, Feb 09, 2011 at 12:09:35PM +1030, Rusty Russell wrote: >> On Wed, 9 Feb 2011 11:23:45 am Michael S. Tsirkin wrote: >> > On Wed, Feb 09, 2011 at 11:07:20AM +1030, Rusty Russell wrote: >> > > On Wed, 2 Feb 2011 03:12:22 pm Michael S. Tsirkin wrote: >> > > > On Wed, Feb 02, 2011 at 10:09:18AM +0530, Krishna Kumar2 wrote: >> > > > > > "Michael S. Tsirkin" <mst@xxxxxxxxxx> 02/02/2011 03:11 AM >> > > > > > >> > > > > > On Tue, Feb 01, 2011 at 01:28:45PM -0800, Shirley Ma wrote: >> > > > > > > On Tue, 2011-02-01 at 23:21 +0200, Michael S. Tsirkin wrote: >> > > > > > > > Confused. We compare capacity to skb frags, no? >> > > > > > > > That's sg I think ... >> > > > > > > >> > > > > > > Current guest kernel use indirect buffers, num_free returns how many >> > > > > > > available descriptors not skb frags. So it's wrong here. >> > > > > > > >> > > > > > > Shirley >> > > > > > >> > > > > > I see. Good point. In other words when we complete the buffer >> > > > > > it was indirect, but when we add a new one we >> > > > > > can not allocate indirect so we consume. >> > > > > > And then we start the queue and add will fail. >> > > > > > I guess we need some kind of API to figure out >> > > > > > whether the buf we complete was indirect? >> > > >> > > I've finally read this thread... I think we need to get more serious >> > > with our stats gathering to diagnose these kind of performance issues. >> > > >> > > This is a start; it should tell us what is actually happening to the >> > > virtio ring(s) without significant performance impact... >> > > >> > > Subject: virtio: CONFIG_VIRTIO_STATS >> > > >> > > For performance problems we'd like to know exactly what the ring looks >> > > like. This patch adds stats indexed by how-full-ring-is; we could extend >> > > it to also record them by how-used-ring-is if we need. >> > > >> > > Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx> >> > >> > Not sure whether the intent is to merge this. If yes - >> > would it make sense to use tracing for this instead? >> > That's what kvm does. >> >> Intent wasn't; I've not used tracepoints before, but maybe we should >> consider a longer-term monitoring solution? >> >> Patch welcome! >> >> Cheers, >> Rusty. > > Sure, I'll look into this. There are several virtio trace events already in QEMU today (see the trace-events file): virtqueue_fill(void *vq, const void *elem, unsigned int len, unsigned int idx) "vq %p elem %p len %u idx %u" virtqueue_flush(void *vq, unsigned int count) "vq %p count %u" virtqueue_pop(void *vq, void *elem, unsigned int in_num, unsigned int out_num) "vq %p elem %p in_num %u out_num %u" virtio_queue_notify(void *vdev, int n, void *vq) "vdev %p n %d vq %p" virtio_irq(void *vq) "vq %p" virtio_notify(void *vdev, void *vq) "vdev %p vq %p" These can be used by building QEMU with a suitable tracing backend like SystemTap (see docs/tracing.txt). Inside the guest I've used dynamic ftrace in the past, although static tracepoints would be nice. 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
