From: Rik van Riel <riel@redhat•com>
To: David Miller <davem@davemloft•net>
Cc: pabeni@redhat•com, eric.dumazet@gmail•com,
netdev@vger•kernel.org, edumazet@google•com, jiri@mellanox•com,
daniel@iogearbox•net, ast@plumgrid•com, aduyck@mirantis•com,
tom@herbertland•com, peterz@infradead•org, mingo@kernel•org,
hannes@stressinduktion•org, linux-kernel@vger•kernel.org
Subject: Re: [RFC PATCH 0/2] net: threadable napi poll loop
Date: Tue, 10 May 2016 17:01:21 -0400 [thread overview]
Message-ID: <1462914081.16365.13.camel@redhat.com> (raw)
In-Reply-To: <20160510.165215.1602157973141296642.davem@davemloft.net>
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On Tue, 2016-05-10 at 16:52 -0400, David Miller wrote:
> From: Rik van Riel <riel@redhat•com>
> Date: Tue, 10 May 2016 16:50:56 -0400
>
> > On Tue, 2016-05-10 at 16:45 -0400, David Miller wrote:
> >> From: Paolo Abeni <pabeni@redhat•com>
> >> Date: Tue, 10 May 2016 22:22:50 +0200
> >>
> >> > On Tue, 2016-05-10 at 09:08 -0700, Eric Dumazet wrote:
> >> >> On Tue, 2016-05-10 at 18:03 +0200, Paolo Abeni wrote:
> >> >>
> >> >> > If a single core host is under network flood, i.e. ksoftirqd
> is
> >> >> > scheduled and it eventually (after processing ~640 packets)
> will
> >> let the
> >> >> > user space process run. The latter will execute a syscall to
> >> receive a
> >> >> > packet, which will have to disable/enable bh at least once
> and
> >> that will
> >> >> > cause the processing of another ~640 packets. To receive a
> >> single packet
> >> >> > in user space, the kernel has to process more than one
> thousand
> >> packets.
> >> >>
> >> >> Looks you found the bug then. Have you tried to fix it ?
> >> ...
> >> > The ksoftirq and the local_bh_enable() design are the root of
> the
> >> > problem, they need to be touched/affected to solve it.
> >>
> >> That's not what I read from your description, processing 640
> packets
> >> before going to ksoftirqd seems to the be the absolute root
> problem.
> >
> > What would a fix for that look like?
> >
> > Keep track of the number of processed incoming packets,
> > and the number of packets handed off, and defer to
> > ksoftirqd earlier if the statistics suggest packets are
> > getting dropped on the floor?
>
> Not by packet count but by something more easily to measure and
> scalable to fairness like processing time.
I need to get back to fixing irq & softirq time accounting,
which does not currently work correctly in all time keeping
modes...
--
All Rights Reversed.
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next prev parent reply other threads:[~2016-05-10 21:01 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-10 14:11 [RFC PATCH 0/2] net: threadable napi poll loop Paolo Abeni
2016-05-10 14:11 ` [RFC PATCH 1/2] net: implement threaded-able napi poll loop support Paolo Abeni
2016-05-10 14:11 ` [RFC PATCH 2/2] net: add sysfs attribute to control napi threaded mode Paolo Abeni
2016-05-10 14:29 ` [RFC PATCH 0/2] net: threadable napi poll loop Eric Dumazet
2016-05-10 15:51 ` David Miller
2016-05-10 16:03 ` Paolo Abeni
2016-05-10 16:08 ` Eric Dumazet
2016-05-10 20:22 ` Paolo Abeni
2016-05-10 20:45 ` David Miller
2016-05-10 20:50 ` Rik van Riel
2016-05-10 20:52 ` David Miller
2016-05-10 21:01 ` Rik van Riel [this message]
2016-05-10 20:46 ` Hannes Frederic Sowa
2016-05-10 21:09 ` Eric Dumazet
2016-05-10 21:31 ` Eric Dumazet
2016-05-10 21:35 ` Rik van Riel
2016-05-10 21:53 ` Eric Dumazet
2016-05-10 22:02 ` Eric Dumazet
2016-05-10 22:44 ` Eric Dumazet
2016-05-10 22:02 ` Rik van Riel
2016-05-11 17:55 ` Eric Dumazet
2016-05-10 22:32 ` Hannes Frederic Sowa
2016-05-10 22:51 ` Eric Dumazet
2016-05-11 6:55 ` Peter Zijlstra
2016-05-11 13:13 ` Hannes Frederic Sowa
2016-05-11 14:40 ` Eric Dumazet
2016-05-11 15:01 ` Rik van Riel
2016-05-11 15:50 ` Eric Dumazet
2016-05-11 21:56 ` Eric Dumazet
2016-05-12 20:07 ` Paolo Abeni
2016-05-12 20:49 ` Eric Dumazet
2016-05-12 20:58 ` Paolo Abeni
2016-05-12 21:05 ` Eric Dumazet
2016-05-13 16:50 ` Paolo Abeni
2016-05-13 17:03 ` Eric Dumazet
2016-05-13 17:19 ` Paolo Abeni
2016-05-13 17:36 ` Eric Dumazet
2016-05-16 13:10 ` Paolo Abeni
2016-05-16 13:38 ` Eric Dumazet
2016-05-11 9:48 ` Paolo Abeni
2016-05-11 13:08 ` Eric Dumazet
2016-05-11 13:39 ` Hannes Frederic Sowa
2016-05-11 13:47 ` Hannes Frederic Sowa
2016-05-11 14:38 ` Paolo Abeni
2016-05-11 14:45 ` Eric Dumazet
2016-05-11 22:47 ` Hannes Frederic Sowa
2016-05-10 15:57 ` Thomas Gleixner
2016-05-10 20:41 ` Paolo Abeni
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