Re: [PATCH] softirq: let ksoftirqd do its job

From	Daniel Borkmann <daniel@iogearbox.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH] softirq: let ksoftirqd do its job
Date	2016-09-23 13:40 +0200
Message-ID	<skwZH-31N-3@gated-at.bofh.it> (permalink)
References	<schO9-5mI-13@gated-at.bofh.it> <schO9-5mI-15@gated-at.bofh.it> <schO9-5mI-1@gated-at.bofh.it> <scQiR-4lP-7@gated-at.bofh.it>
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On 09/02/2016 08:39 AM, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Wed, 31 Aug 2016 10:42:29 -0700
>
>> From: Eric Dumazet <edumazet@google.com>
>>
>> A while back, Paolo and Hannes sent an RFC patch adding threaded-able
>> napi poll loop support : (https://patchwork.ozlabs.org/patch/620657/)
>>
>> The problem seems to be that softirqs are very aggressive and are often
>> handled by the current process, even if we are under stress and that
>> ksoftirqd was scheduled, so that innocent threads would have more chance
>> to make progress.
>>
>> This patch makes sure that if ksoftirq is running, we let it
>> perform the softirq work.
>>
>> Jonathan Corbet summarized the issue in https://lwn.net/Articles/687617/
>>
>> Tested:
>>
>>   - NIC receiving traffic handled by CPU 0
>>   - UDP receiver running on CPU 0, using a single UDP socket.
>>   - Incoming flood of UDP packets targeting the UDP socket.
>>
>> Before the patch, the UDP receiver could almost never get cpu cycles and
>> could only receive ~2,000 packets per second.
>>
>> After the patch, cpu cycles are split 50/50 between user application and
>> ksoftirqd/0, and we can effectively read ~900,000 packets per second,
>> a huge improvement in DOS situation. (Note that more packets are now
>> dropped by the NIC itself, since the BH handlers get less cpu cycles to
>> drain RX ring buffer)
>>
>> Since the load runs in well identified threads context, an admin can
>> more easily tune process scheduling parameters if needed.
>>
>> Reported-by: Paolo Abeni <pabeni@redhat.com>
>> Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
>> Signed-off-by: Eric Dumazet <edumazet@google.com>
>
> I'm just kind of assuming this won't go through my tree, but I can take
> it if that's what everyone agrees to.

Was this actually picked up somewhere in the mean time?

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Re: [PATCH] softirq: let ksoftirqd do its job Daniel Borkmann <daniel@iogearbox.net> - 2016-09-23 13:40 +0200
  Re: [PATCH] softirq: let ksoftirqd do its job Peter Zijlstra <peterz@infradead.org> - 2016-09-23 14:00 +0200
    Re: [PATCH] softirq: let ksoftirqd do its job Jesper Dangaard Brouer <jbrouer@redhat.com> - 2016-09-23 19:00 +0200
      Re: [PATCH] softirq: let ksoftirqd do its job Peter Zijlstra <peterz@infradead.org> - 2016-09-23 23:20 +0200

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