On Thu, Apr 20, 2017 at 11:00:42AM +0200, Jesper Dangaard Brouer wrote: > Hi Linus, > > Just wanted to give a heads-up on two regressions in 4.11-rc series. > > (1) page allocator optimization revert > > Mel Gorman and I have been playing with optimizing the page allocator, > but Tariq spotted that we caused a regression for (NIC) drivers that > refill DMA RX rings in softirq context. > > The end result was a revert, and this is waiting in AKPMs quilt queue: > > http://ozlabs.org/~akpm/mmots/broken-out/revert-mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch > > > (2) Busy softirq can cause userspace not to be scheduled > > I bisected the problem to a499a5a14dbd ("sched/cputime: Increment > kcpustat directly on irqtime account"). See email thread with > Subject: Bisected softirq accounting issue in v4.11-rc1~170^2~28 > http://lkml.kernel.org/r/20170328101403.34a82...@redhat.com > > I don't know the scheduler code well enough to fix this, and will have > to rely others to figure out this scheduler regression. > > To make it clear: I'm only seeing this scheduler regression when a > remote host is sending many many network packets, towards the kernel > which keeps NAPI/softirq busy all the time. A possible hint: tool > "top" only shows this in "si" column, while on v4.10 "top" also blames > "ksoftirqd/N", plus "ps" reported cputime (0:00) seems wrong for ksoftirqd.
(I'm currently working on reproducing that one.)
