On Wed, 2011-02-02 at 22:17 +0200, Michael S. Tsirkin wrote: > Well, this is also the only case where the queue is stopped, no? Yes. I got some debugging data, I saw that sometimes there were so many packets were waiting for free in guest between vhost_signal & guest xmit callback. Looks like the time spent too long from vhost_signal to guest xmit callback? > > I tried to accumulate multiple guest to host notifications for TX > xmits, > > it did help multiple streams TCP_RR results; > I don't see a point to delay used idx update, do you? It might cause per vhost handle_tx processed more packets. > So delaying just signal seems better, right? I think I need to define the test matrix to collect data for TX xmit from guest to host here for different tests. Data to be collected: --------------------- 1. kvm_stat for VM, I/O exits 2. cpu utilization for both guest and host 3. cat /proc/interrupts on guest 4. packets rate from vhost handle_tx per loop 5. guest netif queue stop rate 6. how many packets are waiting for free between vhost signaling and guest callback 7. performance results Test ---- 1. TCP_STREAM single stream test for 1K to 4K message size 2. TCP_RR (64 instance test): 128 - 1K request/response size Different hacks --------------- 1. Base line data ( with the patch to fix capacity check first, free_old_xmit_skbs returns number of skbs) 2. Drop packet data (will put some debugging in generic networking code) 3. Delay guest netif queue wake up until certain descriptors (1/2 ring size, 1/4 ring size...) are available once the queue has stopped. 4. Accumulate more packets per vhost signal in handle_tx? 5. 3 & 4 combinations 6. Accumulate more packets per guest kick() (TCP_RR) by adding a timer? 7. Accumulate more packets per vhost handle_tx() by adding some delay? > Haven't noticed that part, how does your patch make it handle more packets? Added a delay in handle_tx(). What else? It would take sometimes to do this. Shirley -- 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
