linux-kernel - Re: [PATCH 3/4] ipc/sem.c: Always use only one queue for alter operations.

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Date:	Mon, 27 May 2013 14:00:03 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Manfred Spraul <manfred@...orfullife.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Davidlohr Bueso <davidlohr.bueso@...com>, hhuang@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3/4] ipc/sem.c: Always use only one queue for alter operations.

On 05/26/2013 05:08 AM, Manfred Spraul wrote:
> There are two places that can contain alter operations:
> - the global queue: sma->pending_alter
> - the per-semaphore queues: sma->sem_base[].pending_alter.
>
> Since one of the queues must be processed first, this causes an odd
> priorization of the wakeups:
> Right now, complex operations have priority over simple ops.
>
> The patch restores the behavior of linux <=3.0.9: The longest
> waiting operation has the highest priority.
>
> This is done by using only one queue:
> - if there are complex ops, then sma->pending_alter is used.
> - otherwise, the per-semaphore queues are used.
>
> As a side effect, do_smart_update_queue() becomes much simpler:
> No more goto logic.
>
> Signed-off-by: Manfred Spraul <manfred@...orfullife.com>

This is the one where I really wonder whether the
complexity is warranted.

Again, the code does look correct.

Acked-by: Rik van Riel <riel@...hat.com>

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