From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Frederic Weisbecker <fweisbec@gmail.com>
Cc: brouer@redhat.com, Mel Gorman <mgorman@techsingularity.net>,
Tariq Toukan <tariqt@mellanox.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
peterz@infradead.org
Subject: Heads-up: two regressions in v4.11-rc series
Date: Thu, 20 Apr 2017 11:00:42 +0200 [thread overview]
Message-ID: <20170420110042.73d01e0f@redhat.com> (raw)
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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next reply other threads:[~2017-04-20 9:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-20 9:00 Jesper Dangaard Brouer [this message]
2017-04-20 13:25 ` Heads-up: two regressions in v4.11-rc series Frederic Weisbecker
2017-04-20 14:30 ` Mel Gorman
2017-04-21 17:52 ` Linus Torvalds
2017-04-21 20:33 ` Frederic Weisbecker
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