Hi Han and Ben, I changed the FLOW_MISS_MAX_BATCH value to to 1 but the problem still exists. I do see that upcalls are handle individually in userspace. but the RTT of the higher rate are still less than the RTT of the lower rate... Does the ovs kernel use a similar batching mechanism?
On Thu, Jan 16, 2014 at 1:24 PM, Xiaoye Sun <xiaoye....@rice.edu> wrote: > @ Han, I guess FLOW_MISS_MAX_BATCH should be the right place to change. > For my understanding, ovs userspace will batch all the packets it received > and the put packets from same flow into a "group", one group for each flow. > So I guess there are two levels of "batching". > > > > > On Thu, Jan 16, 2014 at 12:17 PM, Zhou, Han <hzh...@ebay.com> wrote: > >> Hi Xiaoye, >> >> > Is there any way to disable this batching mechanism in the ovs kernel >> so that each upcall only contains one packet? >> Batching is a mechanism of the user space upcall handler rather than OVS >> kernel. >> To disable it you can change below macro in ofproto/ofproto-dpif-upcall.h: >> #define FLOW_MISS_MAX_BATCH 50 => 1 >> >> However, I wonder how would batching affect your RTT result. >> On Wed, Jan 15, 2014 at 5:11 PM, Ben Pfaff <b...@nicira.com> wrote: >> > As the rate >> > increases, I guess that a batch contains more than one packet, and >> > it's likely that the batches mix up SYNs and SYN-ACKs, possibly >> > reducing the latency. >> >> @Ben, even if the batches mix up SYNs and SYN-ACKs, they are from >> different >> Flows. For SYN and SYN-ACK pairs of each single flow, they can never be >> mixed in the same batch, because SYN-ACK is not sent out until SYN is >> delivered >> to the receiver. So in my opinion, batching can improve the whole >> throughput but >> cannot explain the better STT. Did I miss anything here? >> >> @Xiaoye, maybe you can change FLOW_MISS_MAX_BATCH to different numbers to >> verify. >> >> Best regards, >> Han >> _______________________________________________ >> discuss mailing list >> discuss@openvswitch.org >> http://openvswitch.org/mailman/listinfo/discuss >> >> > > > -- > Xiaoye (Steven) Sun, Ph.D. Student > Department of Electrical and Computer Engineering (ECE) & Department of > Computer Science (CS) > George R. Brown School of Engineering > Rice University, Houston, Texas, USA > -- Xiaoye (Steven) Sun, Ph.D. Student Department of Electrical and Computer Engineering (ECE) & Department of Computer Science (CS) George R. Brown School of Engineering Rice University, Houston, Texas, USA
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