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

From: Peter Zijlstra
Date: Sat Oct 01 2011 - 09:04:21 EST

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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