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    SubjectHeads-up: two regressions in v4.11-rc series
    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/20170328101403.34a82fbf@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.


    --
    Best regards,
    Jesper Dangaard Brouer
    MSc.CS, Principal Kernel Engineer at Red Hat
    LinkedIn: http://www.linkedin.com/in/brouer

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