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

[Daniel Borkmann]

On 09/02/2016 08:39 AM, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> Date: Wed, 31 Aug 2016 10:42:29 -0700
>
> > From: Eric Dumazet <edumazet@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > Reported-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> 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?