On Tue, 12 Oct 2010 16:31:36 +0200 Jean-Michel Hautbois <jhautbois@xxxxxxxxx> wrote: > Hi there ! > > I am facing a jitter issue that I will try to explain : > I have the following configuration : > > (A) eth0 <--> br0 <--> eth1 (B) > > I have a small and custom kernel (I removed netfilter, for instance) and I > am measuring the time between A and B (using hardware taps, etc.). > My bandwidth is quite small (each packet is about 200 bytes and there is a > delay of 10ms between each packet). > I am measuring both the latency and the jitter (max_latency - min_latency) > and this one is quite large. > > I added ftrace option, and after some (long) investigations, I am currently > limiting my study to the bridge part. > > When I trace only br_handle_frame and br_forward_finish and do my test on > 6500 frames I have : > - average latency of 39µs > - minimum latency of 34 µs > - maximum latency of 81µs > > Thus, my jitter is 47µs. > This may seem low, but this is about two to three times what I expect and I > cannot see why a bridge which is only forwarding a frame would have jitter ? > If you have any idea, everything is interesting for me. > I thought maybe to skb_clone ? > > Best Regards, > JM You probably have NAPI and/or interrupt coalescing setting enabled on one or both of the devices. -- _______________________________________________ Bridge mailing list Bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/bridge
