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Date:	Fri, 21 Mar 2014 02:45:47 +0000
From:	"Dilger, Andreas" <andreas.dilger@...el.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Peng Tao <bergwolf@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"Drokin, Oleg" <oleg.drokin@...el.com>
Subject: Re: [PATCH 0/2] wait: introduce WQ_FLAG_EXCLUSIVE_HEAD

On 2014/03/20, 11:51 AM, "Oleg Nesterov" <oleg@...hat.com> wrote:

>On 03/19, Oleg Nesterov wrote:
>>
>> OK, I'll try to test/cleanup/resend tomorrow.
>
>Cough. Still un-tested, sorry. I will test it somehow and report,
>but I'd like to send this for review right now.
>
>Because I simply can't decide what the new flag should actually
>do, so please ack/nack the semantics/naming at least.
>
>Changes:
>
>	1. I decided it would be better to change __wait_event()
>	   to accept wait.flags right now. This looks better in
>	   any case to me, and otherwise we need to introduce the
>	   __wait_exclusive_enum.
>
>	   The change looks trivial (both actually), please tell
>	   me if you think it doesn't deserve a separate patch.
>
>	2. I won't insist, but WQ_FLAG_EXCLUSIVE_HEAD can be used
>	   without WQ_FLAG_EXCLUSIVE.
>
>	   Unlikely this can be useful, but it looks more natural
>	   this way. Otherwise we need to add another check to
>	   ensure that WQ_FLAG_EXCLUSIVE_HEAD can't come alone.
>
>	   However, perhaps this means the new flag needs another
>	   name. I agree in advance with any.

What about:

#define WQ_FLAG_HEAD	0x02

#define WQ_FLAG_EXCLUSIVE_HEAD (WQ_FLAG_HEAD | WQ_FLAG_EXCLUSIVE)

That avoids having WQ_FLAG_EXCLUSIVE_HEAD not actually meaning "exclusive"?

Patches look reasonable at first glance.  The second patch would need
to be changed to handle that WQ_FLAG_EXCLUSIVE_HEAD has both bits set
(probably just replace uses of WQ_FLAG_EXCLUSIVE_HEAD with WQ_FLAG_HEAD).

Cheers, Andreas
-- 
Andreas Dilger

Lustre Software Architect
Intel High Performance Data Division


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