From: Jason Xing <kerneljasonxing@gmail.com>
To: Paolo Abeni <pabeni@redhat.com>
Cc: Jakub Kicinski <kuba@kernel.org>,
peterz@infradead.org, tglx@linutronix.de, jstultz@google.com,
edumazet@google.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] softirq: uncontroversial change
Date: Fri, 21 Apr 2023 17:46:58 +0800 [thread overview]
Message-ID: <CAL+tcoDZxssH-s08_LO2_=HqYJ77w_N-avOmEWQ4AiiprHFmXw@mail.gmail.com> (raw)
In-Reply-To: <140f61e2e1fcb8cf53619709046e312e343b53ca.camel@redhat.com>
On Fri, Apr 21, 2023 at 5:33 PM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Fri, 2023-04-21 at 10:48 +0800, Jason Xing wrote:
> >
> > > My understanding is that we want to avoid adding more heuristics here,
> > > preferring a consistent refactor.
> > >
> > > I would like to propose a revert of:
> > >
> > > 4cd13c21b207 softirq: Let ksoftirqd do its job
> > >
> > > the its follow-ups:
> > >
> > > 3c53776e29f8 Mark HI and TASKLET softirq synchronous
> > > 0f50524789fc softirq: Don't skip softirq execution when softirq thread is parking
> >
> > More than this, I list some related patches mentioned in the above
> > commit 3c53776e29f8:
> > 1ff688209e2e ("watchdog: core: make sure the watchdog_worker is not deferred")
> > 8d5755b3f77b ("watchdog: softdog: fire watchdog even if softirqs do
> > not get to run")
> > 217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()")
>
[...]
> The first 2 changes replace plain timers with HR ones, could possibly
> be reverted, too, but it should not be a big deal either way.
>
> I think instead we want to keep the third commit above, as it should be
> useful when napi threaded is enabled.
>
> Generally speaking I would keep the initial revert to the bare minimum.
I agree with you :)
>
> > > The problem originally addressed by 4cd13c21b207 can now be tackled
> > > with the threaded napi, available since:
> > >
> > > 29863d41bb6e net: implement threaded-able napi poll loop support
> > >
> > > Reverting the mentioned commit should address the latency issues
> > > mentioned by Jakub - I verified it solves a somewhat related problem in
> > > my setup - and reduces the layering of heuristics in this area.
> >
> > Sure, it is. I also can verify its usefulness in the real workload.
> > Some days ago I also sent a heuristics patch [1] that can bypass the
> > ksoftirqd if the user chooses to mask some type of softirq. Let the
> > user decide it.
> >
> > But I observed that if we mask some softirqs, or we can say,
> > completely revert the commit 4cd13c21b207, the load would go higher
> > and the kernel itself may occupy/consume more time than before. They
> > were tested under the similar workload launched by our applications.
> >
> > [1]: https://lore.kernel.org/all/20230410023041.49857-1-kerneljasonxing@gmail.com/
>
> Thanks for the reference, I would have missed that patch otherwise.
>
> My understanding is that adding more knobs here is in the opposite
> direction of what Thomas is suggesting, and IMHO the 'now mask' should
> not be exposed to user-space.
Could you please share the link about what Thomas is suggesting? I
missed it. At the beginning, I didn't have the guts to revert the
commit directly. Instead I wrote a compromised patch that is not that
elegant as you said. Anyway, the idea is common, but reverting the
whole commit may involve more work. I will spend some time digging
into this part.
More suggestions are also welcome :)
Thanks,
Jason
>
> >
> Thanks for the feedback,
>
> Paolo
>
next prev parent reply other threads:[~2023-04-21 9:48 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-22 22:12 [PATCH 0/3] softirq: uncontroversial change Jakub Kicinski
2022-12-22 22:12 ` [PATCH 1/3] softirq: rename ksoftirqd_running() -> ksoftirqd_should_handle() Jakub Kicinski
2022-12-22 22:12 ` [PATCH 2/3] softirq: avoid spurious stalls due to need_resched() Jakub Kicinski
2023-01-31 22:32 ` Jakub Kicinski
2023-03-03 13:30 ` Thomas Gleixner
2023-03-03 15:18 ` Thomas Gleixner
2023-03-03 21:31 ` Jakub Kicinski
2023-03-03 22:37 ` Paul E. McKenney
2023-03-03 23:25 ` Dave Taht
2023-03-04 1:14 ` Paul E. McKenney
2023-03-03 23:36 ` Paul E. McKenney
2023-03-03 23:44 ` Jakub Kicinski
2023-03-04 1:25 ` Paul E. McKenney
2023-03-04 1:39 ` Jakub Kicinski
2023-03-04 3:11 ` Paul E. McKenney
2023-03-04 20:48 ` Paul E. McKenney
2023-03-05 20:43 ` Thomas Gleixner
2023-03-05 22:42 ` Paul E. McKenney
2023-03-05 23:00 ` Frederic Weisbecker
2023-03-06 4:30 ` Paul E. McKenney
2023-03-06 11:22 ` Frederic Weisbecker
2023-03-06 9:13 ` David Laight
2023-03-06 11:57 ` Frederic Weisbecker
2023-03-06 14:57 ` Paul E. McKenney
2023-03-07 0:51 ` Jakub Kicinski
2022-12-22 22:12 ` [PATCH 3/3] softirq: don't yield if only expedited handlers are pending Jakub Kicinski
2023-01-09 9:44 ` Peter Zijlstra
2023-01-09 10:16 ` Eric Dumazet
2023-01-09 19:12 ` Jakub Kicinski
2023-03-03 11:41 ` Thomas Gleixner
2023-03-03 14:17 ` Thomas Gleixner
2023-04-20 17:24 ` [PATCH 0/3] softirq: uncontroversial change Paolo Abeni
2023-04-20 17:41 ` Eric Dumazet
2023-04-20 20:23 ` Paolo Abeni
2023-04-21 2:48 ` Jason Xing
2023-04-21 9:33 ` Paolo Abeni
2023-04-21 9:46 ` Jason Xing [this message]
2023-05-09 19:56 ` [tip: irq/core] Revert "softirq: Let ksoftirqd do its job" tip-bot2 for Paolo Abeni
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