On Wed, 2011-02-02 at 23:20 +0200, Michael S. Tsirkin wrote: > > 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) Since I found that the netif queue stop/wake up is so expensive, I created a dropping packets patch on guest side so I don't need to debug generic networking code. guest start_xmit() capacity = free_old_xmit_skb() + virtqueue_get_num_freed() if (capacity == 0) drop this packet; return; In the patch, both guest TX interrupts and callback have been omitted. Host vhost_signal in handle_tx can totally be removed as well. (A new virtio_ring API is needed for exporting total of num_free descriptors here -- virtioqueue_get_num_freed) Initial TCP_STREAM performance results I got for guest to local host 4.2Gb/s for 1K message size, (vs. 2.5Gb/s) 6.2Gb/s for 2K message size, and (vs. 3.8Gb/s) 9.8Gb/s for 4K message size. (vs.5.xGb/s) Since large message size (64K) doesn't hit (capacity == 0) case, so the performance only has a little better. (from 13.xGb/s to 14.x Gb/s) kvm_stat output shows significant exits reduction for both VM and I/O, no guest TX interrupts. With dropping packets, TCP retrans has been increased here, so I can see performance numbers are various. This might be not a good solution, but it gave us some ideas on expensive netif queue stop/wake up between guest and host notification. I couldn't find a better solution on how to reduce netif queue stop/wake up rate for small message size. But I think once we can address this, the guest TX performance will burst for small message size. I also compared this with return TX_BUSY approach when (capacity == 0), it is not as good as dropping packets. > > 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 > > > Need to think about this. > > -- 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
