On 08/20/2013 10:33 AM, Jason Wang wrote: > On 08/16/2013 05:54 PM, Michael S. Tsirkin wrote: >> On Fri, Aug 16, 2013 at 01:16:26PM +0800, Jason Wang wrote: >>>> Switch to use vhost_add_used_and_signal_n() to avoid multiple calls to >>>> vhost_add_used_and_signal(). With the patch we will call at most 2 times >>>> (consider done_idx warp around) compared to N times w/o this patch. >>>> >>>> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> >> So? Does this help performance then? >> > Looks like it can especially when guest does support event index. When > guest enable tx interrupt, this can saves us some unnecessary signal to > guest. I will do some test. Have done some test. I can see 2% - 3% increasing in both aggregate transaction rate and per cpu transaction rate in TCP_RR and UDP_RR test. I'm using ixgbe. W/o this patch, I can see more than 100 calls of vhost_add_used_signal() in one vhost_zerocopy_signaled_used(). This is because ixgbe (and other modern ethernet driver) tends to free old tx skbs in a loop during tx interrupt, and vhost tend to batch the adding used and signal in vhost_zerocopy_callback(). Switching to use vhost_add_use_and_signal_n() means saving 100 times of used idx updating and memory barriers. -- 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
