Thanks Ben, You are probably right. In the function of handle_miss_upcalls() in file /ofproto/ofproto-dpif.c, I print out n_misses, which represents the number of packet in each kernel upcall. and I found that there will be more packets in an upcall when the packet rate is higher.
Is there any way to disable this batching mechanism in the ovs kernel so that each upcall only contains one packet? Thanks! On Wed, Jan 15, 2014 at 5:11 PM, Ben Pfaff <[email protected]> wrote: > On Wed, Jan 15, 2014 at 04:56:02PM -0600, Xiaoye Sun wrote: > > In the experiment, I change the sending rate of the syn packet and > compute > > the RTT of each syn and syn-ack pair. However, I found that when the rate > > is high, for example, 200 syn pkt per sec, the RTTs usually are much less > > than the RTTs of a lower sending rate, for example 50 pkt per sec. > > > > This result is strange since when the sending rate is high, the > controller > > and ovs should have more workload. The RTT should not be less than the > RTT > > in a network having less workload per second... > > OVS tries to deal with packets in batches for efficiency. At a low > rate, probably each batch contains exactly one packet. 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. > > OVS 2.0 and later probably have much better latency because these > versions use separate threads dedicated to packet forwarding. > _______________________________________________ > discuss mailing list > [email protected] > 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
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