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:
(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
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.
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat