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Date: Thu, 6 Aug 2009 04:40:37 -0700
Message-ID: <6599ad830908060440g2f6cbed6xdc54c7096cd3745e@mail.gmail.com>
Subject: Re: [PATCH 6/6] Makes procs file writable to move all threads by tgid 
	at once
From: Paul Menage <menage@google.com>
To: Paul Menage <menage@google.com>, Benjamin Blum <bblum@google.com>,
       containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
       akpm@linux-foundation.org, Peter Zijlstra <a.p.zijlstra@chello.nl>
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On Thu, Aug 6, 2009 at 4:24 AM, Louis Rilling<Louis.Rilling@kerlabs.com> wrote:
>
> You meant signal_struct, right? sighand_struct can be shared by several
> thread groups, while signal_struct can't.
>

No, I meant sighand_struct. I realise that it *can* be shared between
processes, but I didn't think that NPTL actually did so. (Are there
common cases of this happening?) And in cases where it was shared, it
wouldn't affect correctness, but simply create the potential for a
little more contention.

I agree that signal_struct might in principle be a better place for
it, but the first cacheline of signal_struct appears to be occupied
with performance-sensitive things (a couple of counters and a queue
used in do_wait()) already, whereas the first cacheline of
sighand_struct only appears to be used incremented/decremented during
fork/exit, and when delivering a bunch of mostly-fatal signals.

But having said that, if having it in signal_struct isn't considered a
potential performance hit, it would be fine there too.

Paul