From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Matt Fleming <matt@console-pimps.org>,
Tejun Heo <htejun@gmail.com>,
linux-kernel@vger.kernel.org, Tony Luck <tony.luck@intel.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [RFC][PATCH 0/5] Signal scalability series
Date: Mon, 03 Oct 2011 17:22:00 +0200 [thread overview]
Message-ID: <1317655320.20367.25.camel@twins> (raw)
In-Reply-To: <20111003130701.GB25952@redhat.com>
On Mon, 2011-10-03 at 15:07 +0200, Oleg Nesterov wrote:
> On 10/01, Peter Zijlstra wrote:
> But this series can't help afaics. At least in its current state. It
> only adds more locking to the sending paths.
Right, so I was hoping Matt had a plan (TM)... :-)
> And anyway it is wrong (afaics, and I didn't read it yet ;).
I'll leave you to be the judge of that, I haven't bent by brain around
all this signal stuff yet..
> > which precludes being able
> > to deliver signals from hardirq context, leading to lots of ugly in -rt.
>
> I think, the best solution would be: never send the signal from irq
> context, and ->siglock shouldn't disable irqs.
Bit hard that, posix timers need to deliver signals which pretty much
mandates we do something from irq context (and the round-trip through
softirq context really isn't pretty nor good for performance).
> > The hope is that this work is a stepping stone to O(1) signal delivery.
>
> Probably this is possible too. I was thinking anout this when
> set_current_blocked() was added. Unfortunately this needs a lot of
> complications.
Right, so the thing Thomas and I have been promoting for a while now is
to update a signal target vector on every signal mask update. Mask
updates should be the slow path. This would leave us with a ready target
in O(1).
Although given that we've promoted this idea for a while now and it
hasn't happened yet I'm sure its non-trivial :-)
> > Breaking up the multitude of uses of siglock certainly seems worthwhile
> > esp.
>
> Agreed. But I am not sure how much we should split the locking when
> it comes to sending/dequeueing/etc signals. 5 locks seems too much.
It doesn't need all 5 locks to send a signal, does it? But then, I'm
somewhat out of my depth here, the whole signal delivery path always
looses me.
> > 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.
>
> True.
>
> Mostly this is because we moved misc stuff from tasklist to siglock,
> previously this was a win. Today this doesn't look good.
Well a per-process lock still wins from a global lock, but yeah, it
wants to be broken up further.
next prev parent reply other threads:[~2011-10-03 15:23 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
2011-10-04 7:37 ` Tejun Heo
2011-10-03 13:07 ` Oleg Nesterov
2011-10-03 15:22 ` Peter Zijlstra [this message]
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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