From: Thomas Gleixner <tglx@linutronix.de>
To: Tejun Heo <htejun@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
Matt Fleming <matt@console-pimps.org>,
Oleg Nesterov <oleg@redhat.com>,
linux-kernel@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
akpm@linux-foundation.org, torvalds@linux-foundation.org
Subject: Re: [RFC][PATCH 0/5] Signal scalability series
Date: Mon, 3 Oct 2011 15:56:26 +0200 (CEST) [thread overview]
Message-ID: <alpine.LFD.2.02.1110031544340.1489@ionos> (raw)
In-Reply-To: <20111003013855.GG31799@mtj.dyndns.org>
On Sun, 2 Oct 2011, Tejun Heo wrote:
> On Sat, Oct 01, 2011 at 03:03:29PM +0200, Peter Zijlstra wrote:
> > On Sat, 2011-10-01 at 11:16 +0100, Matt Fleming wrote:
> > > I also think Thomas/Peter mentioned something about latency in
> > > delivering timer signals because of contention on the per-process
> > > siglock. They might have some more details on that.
> >
> > Right, so signal delivery is O(nr_threads), which precludes being able
> > to deliver signals from hardirq context, leading to lots of ugly in -rt.
>
> Signal delivery is O(#threads)? Delivery of fatal signal is of course
> but where do we walk all threads during non-fatal signal deliveries?
> What am I missing?
Delivery of any process wide signal can result in an O(thread) walk to
find a valid target. That's true for user space originated and kernel
space originated (e.g. posix timers) signals.
> > Breaking up the multitude of uses of siglock certainly seems worthwhile
> > esp. if it also allows for a cleanup of the horrid mess called
> > signal_struct (which really should be called process_struct or so).
> >
> > And yes, aside from that the siglock can be quite contended because its
> > pretty much the one lock serializing all of the process wide state.
>
> Hmmm... can you please be a bit more specific? I personally has never
> seen a case where siglock becomes a problem and IIUC Matt also doesn't
Signal heavy applications suffer massivly from sighand->siglock
contention. sighand->siglock protects the world and some more and Matt
has explained it quite proper. And we have rather large code pathes
covered by it (posix-cpu-timers are the worst of all).
> have actual use case at hand. Given the fragile nature of this part
> of kernel, it would be nice to know what the return is.
The return is finer grained locking and in the end a faster signal
delivery path which benefits everyone as we do not burden a random
interrupted task with the convoluted signal delivery because we want
to burden the task using signals with it.
Thanks,
tglx
next prev parent reply other threads:[~2011-10-03 13:56 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-30 15:12 [RFC][PATCH 0/5] Signal scalability series Matt Fleming
2011-09-30 15:12 ` [RFC][PATCH 1/5] signal: Document signal locking rules Matt Fleming
2011-09-30 15:12 ` [RFC][PATCH 2/5] signal: Add rwlock to protect sighand->action Matt Fleming
2011-09-30 15:25 ` Peter Zijlstra
2011-09-30 15:56 ` Matt Fleming
2011-09-30 15:12 ` [RFC][PATCH 3/5] signal: Reduce sighand->siglock hold time in get_signal_to_deliver() Matt Fleming
2011-09-30 15:12 ` [RFC][PATCH 4/5] signal: Add signal->ctrl_lock for job control Matt Fleming
2011-09-30 15:30 ` Peter Zijlstra
2011-09-30 15:36 ` Matt Fleming
2011-09-30 15:12 ` [RFC][PATCH 5/5] signal: Split siglock into shared_siglock and per-thread siglock Matt Fleming
2011-09-30 16:52 ` [RFC][PATCH 0/5] Signal scalability series Oleg Nesterov
2011-09-30 18:54 ` Oleg Nesterov
2011-09-30 20:00 ` Matt Fleming
2011-09-30 23:56 ` Tejun Heo
2011-10-01 10:16 ` Matt Fleming
2011-10-01 13:03 ` Peter Zijlstra
2011-10-03 1:38 ` Tejun Heo
2011-10-03 13:56 ` Thomas Gleixner [this message]
2011-10-04 7:37 ` Tejun Heo
2011-10-03 13:07 ` Oleg Nesterov
2011-10-03 15:22 ` Peter Zijlstra
2011-10-04 17:14 ` Oleg Nesterov
2011-10-04 17:52 ` Oleg Nesterov
2011-10-04 17:54 ` Linus Torvalds
2011-10-04 18:13 ` Oleg Nesterov
2011-10-03 13:16 ` Oleg Nesterov
2011-10-04 8:56 ` Matt Fleming
2011-10-04 17:29 ` Oleg Nesterov
2011-09-30 22:30 ` Andi Kleen
2011-10-01 9:35 ` Matt Fleming
2011-10-03 15:28 ` Linus Torvalds
2011-10-03 15:43 ` Matt Fleming
2011-10-03 16:35 ` Oleg Nesterov
2011-10-03 20:58 ` Matt Fleming
2011-10-03 21:45 ` Linus Torvalds
2011-10-03 22:13 ` Thomas Gleixner
2011-10-04 8:20 ` Matt Fleming
2011-10-04 17:39 ` Oleg Nesterov
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