From: Paolo Abeni <pab...@redhat.com> Date: Tue, 23 Jan 2018 11:13:52 +0100
> Hi, > > On Fri, 2018-01-19 at 16:46 +0100, Frederic Weisbecker wrote: >> As per Linus suggestion, this take doesn't limit the number of occurences >> per jiffy anymore but instead defers a vector to workqueues as soon as >> it gets re-enqueued on IRQ tail. >> >> No tunable here, so testing should be easier. >> >> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git >> softirq/thread-v3 >> >> HEAD: 6835e92cbd70ef4a056987d2e1ed383b294429d4 > > I tested this series in the UDP flood scenario, binding the user space > process receiving the packets on the same CPU processing the related > IRQ, and the tput sinks nearly to 0, like before Eric's patch. > > The perf tool says that almost all the softirq processing is done > inside the workqueue, but the user space process is scheduled very > rarely, while before this series, in this scenario, ksoftirqd and the > user space process got a fair share of the CPU time. Do workqueue threads get a higher scheduling priority than user processes? If so, that's going to work against the entire point of deferring softirq work into a thread. Or is it that the workqueue execution is simply not yielding for some reason?
