From: Rik van Riel <r...@redhat.com> Date: Tue, 10 May 2016 16:50:56 -0400
> On Tue, 2016-05-10 at 16:45 -0400, David Miller wrote: >> From: Paolo Abeni <pab...@redhat.com> >> Date: Tue, 10 May 2016 22:22:50 +0200 >> >> > On Tue, 2016-05-10 at 09:08 -0700, Eric Dumazet wrote: >> >> On Tue, 2016-05-10 at 18:03 +0200, Paolo Abeni wrote: >> >> >> >> > If a single core host is under network flood, i.e. ksoftirqd is >> >> > scheduled and it eventually (after processing ~640 packets) will >> let the >> >> > user space process run. The latter will execute a syscall to >> receive a >> >> > packet, which will have to disable/enable bh at least once and >> that will >> >> > cause the processing of another ~640 packets. To receive a >> single packet >> >> > in user space, the kernel has to process more than one thousand >> packets. >> >> >> >> Looks you found the bug then. Have you tried to fix it ? >> ... >> > The ksoftirq and the local_bh_enable() design are the root of the >> > problem, they need to be touched/affected to solve it. >> >> That's not what I read from your description, processing 640 packets >> before going to ksoftirqd seems to the be the absolute root problem. > > What would a fix for that look like? > > Keep track of the number of processed incoming packets, > and the number of packets handed off, and defer to > ksoftirqd earlier if the statistics suggest packets are > getting dropped on the floor? Not by packet count but by something more easily to measure and scalable to fairness like processing time.
