On Thu, Jan 11, 2018 at 12:16 PM, Eric Dumazet <eduma...@google.com> wrote: > > Note that when I implemented TCP Small queues, I did experiments between > using a work queue or a tasklet, and workqueues added unacceptable P99 > latencies, when many user threads are competing with kernel threads.
Yes. So I think one solution might be to have a hybrid system, where we do the softirq's synchronously normally (which is what you really want for good latency). But then fall down on a threaded model - but that fallback case should be per-softirq, not global. So if one softirq uses a lot of CPU time, that shouldn't affect the latency of other softirqs. So maybe we could get rid of the per-cpu ksoftirqd entirely, and replace it with with per-cpu and per-softirq workqueues? Would something like that sound sane? Just a SMOP/SMOT (small matter of programming/testing). Linus