linux-kernel - Re: [PATCH] ipc/msg: Implement lockless pipelined wakeups

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Message-ID: <563595C3.5090609@colorfullife.com>
Date:	Sun, 1 Nov 2015 05:32:03 +0100
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org
Cc:	Davidlohr Bueso <dave@...olabs.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	George Spelvin <linux@...izon.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] ipc/msg: Implement lockless pipelined wakeups

Hi Sebastian,

On 10/30/2015 12:26 PM, Sebastian Andrzej Siewior wrote:
> This patch moves the wakeup_process() invocation so it is not done under
> the perm->lock by making use of a lockless wake_q. With this change, the
> waiter is woken up once the message has been assigned and it does not
> need to loop on SMP if the message points to NULL. In the signal case we
> still need to check the pointer under the lock to verify the state.
>
> This change should also avoid the introduction of preempt_disable() in
> -RT which avoids a busy-loop which pools for the NULL -> !NULL
> change if the waiter has a higher priority compared to the waker.
with regards to functional tests:
fakeroot is a heavy system V user (at least if it is configured for sysv).
"make -j" under fakeroot was a useful stresstest

with regards to benchmarks:
I've attached one of my files.

Otherwise: Nice!

--
     Manfred


View attachment "pmsg-shared.cpp" of type "text/x-c++src" (5188 bytes)