linux-kernel - Re: [RFC][PATCH 0/5] Signal scalability series

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Date:	Sat, 01 Oct 2011 15:03:29 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	Tejun Heo <htejun@...il.com>, Oleg Nesterov <oleg@...hat.com>,
	linux-kernel@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH 0/5] Signal scalability series

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.

The hope is that this work is a stepping stone to O(1) signal delivery.

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.
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