linux-kernel - Re: [patch] shared tag queue barrier comment

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Message-ID: <20070914070020.GU25592@kernel.dk>
Date:	Fri, 14 Sep 2007 09:00:20 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] shared tag queue barrier comment

On Fri, Sep 14 2007, Nick Piggin wrote:
> 
> Should add some comments for the tag barriers (they won't be so important
> if we can switch over to the explicit _lock bitops, but for now we should
> make it clear).

Thanks!

> Jens' original patch said a barrier after the test_and_clear_bit was also
> required. I can't see why (and it would prevent the use of the _lock bitop).

Yeah, I don't think it's needed either. The important bit was ordering
the ->tag_index[tag] = NULL setting before clearing the bit, and as long
as those two operations are ordered, we are good to go. So the last
memory barrier was not needed.

-- 
Jens Axboe

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