From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Yan Zhai <yan@cloudflare.com>,
Eric Dumazet <edumazet@google.com>,
Network Development <netdev@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>, Jiri Pirko <jiri@resnulli.us>,
Simon Horman <horms@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Lorenzo Bianconi <lorenzo@kernel.org>,
Coco Li <lixiaoyan@google.com>, Wei Wang <weiwan@google.com>,
Alexander Duyck <alexanderduyck@fb.com>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
LKML <linux-kernel@vger.kernel.org>,
rcu@vger.kernel.org, bpf <bpf@vger.kernel.org>,
kernel-team <kernel-team@cloudflare.com>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH] net: raise RCU qs after each threaded NAPI poll
Date: Wed, 28 Feb 2024 14:48:44 -0800 [thread overview]
Message-ID: <CAADnVQ+szRDGaDJPoBFR9KyeMjwpuxOCNys=yxDaCLYZkSkyYw@mail.gmail.com> (raw)
In-Reply-To: <20240228173307.529d11ee@gandalf.local.home>
On Wed, Feb 28, 2024 at 2:31 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Wed, 28 Feb 2024 14:19:11 -0800
> "Paul E. McKenney" <paulmck@kernel.org> wrote:
>
> > > >
> > > > Well, to your initial point, cond_resched() does eventually invoke
> > > > preempt_schedule_common(), so you are quite correct that as far as
> > > > Tasks RCU is concerned, cond_resched() is not a quiescent state.
> > >
> > > Thanks for confirming. :-)
> >
> > However, given that the current Tasks RCU use cases wait for trampolines
> > to be evacuated, Tasks RCU could make the choice that cond_resched()
> > be a quiescent state, for example, by adjusting rcu_all_qs() and
> > .rcu_urgent_qs accordingly.
> >
> > But this seems less pressing given the chance that cond_resched() might
> > go away in favor of lazy preemption.
>
> Although cond_resched() is technically a "preemption point" and not truly a
> voluntary schedule, I would be happy to state that it's not allowed to be
> called from trampolines, or their callbacks. Now the question is, does BPF
> programs ever call cond_resched()? I don't think they do.
>
> [ Added Alexei ]
I'm a bit lost in this thread :)
Just answering the above question.
bpf progs never call cond_resched() directly.
But there are sleepable (aka faultable) bpf progs that
can call some helper or kfunc that may call cond_resched()
in some path.
sleepable bpf progs are protected by rcu_tasks_trace.
That's a very different one vs rcu_tasks.
next prev parent reply other threads:[~2024-02-28 22:48 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-27 15:44 [PATCH] net: raise RCU qs after each threaded NAPI poll Yan Zhai
2024-02-27 16:44 ` Eric Dumazet
2024-02-27 18:32 ` Paul E. McKenney
2024-02-27 21:22 ` Yan Zhai
2024-02-27 22:58 ` Paul E. McKenney
2024-02-28 3:10 ` Jakub Kicinski
2024-02-28 4:42 ` Paul E. McKenney
2024-02-28 14:43 ` Jakub Kicinski
2024-02-28 15:15 ` Paul E. McKenney
2024-02-28 15:35 ` Jakub Kicinski
2024-02-28 15:57 ` Yan Zhai
2024-02-28 11:50 ` Toke Høiland-Jørgensen
2024-02-28 15:10 ` Paul E. McKenney
2024-02-28 15:48 ` Yan Zhai
2024-02-28 17:47 ` Paul E. McKenney
2024-02-28 15:37 ` Joel Fernandes
2024-02-28 16:37 ` Yan Zhai
2024-02-28 17:18 ` Paul E. McKenney
2024-02-28 20:14 ` Joel Fernandes
2024-02-28 21:13 ` Paul E. McKenney
2024-02-28 21:27 ` Joel Fernandes
2024-02-28 21:52 ` Paul E. McKenney
2024-02-28 22:10 ` Joel Fernandes
2024-02-28 22:19 ` Paul E. McKenney
2024-02-28 22:33 ` Steven Rostedt
2024-02-28 22:48 ` Alexei Starovoitov [this message]
2024-02-28 22:58 ` Paul E. McKenney
2024-02-29 14:21 ` Joel Fernandes
2024-02-29 16:57 ` Paul E. McKenney
2024-02-29 17:41 ` Joel Fernandes
2024-02-29 18:29 ` Paul E. McKenney
2024-03-02 2:24 ` Joel Fernandes
2024-03-03 0:25 ` Paul E. McKenney
2024-03-03 1:01 ` Joel Fernandes
2024-03-04 9:16 ` Joel Fernandes
2024-03-05 17:53 ` Paul E. McKenney
2024-03-05 19:57 ` Mark Rutland
2024-03-05 21:52 ` Paul E. McKenney
2024-03-06 16:56 ` Steven Rostedt
2024-03-07 16:57 ` Mark Rutland
2024-03-07 18:34 ` Mark Rutland
2024-03-07 18:52 ` Steven Rostedt
2024-03-07 18:58 ` Paul E. McKenney
2024-03-04 9:16 ` Joel Fernandes
2024-02-28 22:49 ` Paul E. McKenney
2024-02-27 21:17 ` Yan Zhai
2024-02-28 23:53 ` Yan Zhai
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