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From: Kent Overstreet <kmo@daterainc.com>
To: Shaohua Li <shli@kernel.org>
Cc: linux-kernel@vger.kernel.org, axboe@kernel.dk, hch@infradead.org
Subject: Re: [patch 1/2]percpu_ida: fix a live lock
Date: Sat, 4 Jan 2014 13:08:04 -0800	[thread overview]
Message-ID: <20140104210804.GA24199@kmo-pixel> (raw)
In-Reply-To: <20131231033827.GA31994@kernel.org>

On Tue, Dec 31, 2013 at 11:38:27AM +0800, Shaohua Li wrote:
> 
> steal_tags only happens when free tags is more than half of the total tags.
> This is too restrict and can cause live lock. I found one cpu has free tags,
> but other cpu can't steal (thread is bound to specific cpus), threads which
> wants to allocate tags are always sleeping. I found this when I run next patch,
> but this could happen without it I think.
> 
> I did performance test too with null_blk. Two cases (each cpu has enough percpu
> tags, or total tags are limited) haven't performance changes.

This doesn't appear to me to fix anything wrong with the current code
(and it'll hurt performance) - we explicitly don't guarantee that all
the tags will be available for allocation at any given time, only half
of them. Can you explain more how this is being used where you're seeing
the issue? And I don't see the other patch in your patch series.

  reply	other threads:[~2014-01-04 21:06 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-12-31  3:38 [patch 1/2]percpu_ida: fix a live lock Shaohua Li
2014-01-04 21:08 ` Kent Overstreet [this message]
2014-01-05 13:13   ` Shaohua Li
2014-01-06 20:46     ` Kent Overstreet
2014-01-06 20:52       ` Jens Axboe
2014-01-06 21:47         ` Kent Overstreet
2014-02-09 15:50           ` Alexander Gordeev
2014-02-10 10:32             ` Christoph Hellwig
2014-02-10 12:29               ` Alexander Gordeev
2014-02-10 15:49                 ` Alexander Gordeev
2014-02-10 16:16                   ` Christoph Hellwig
2014-02-10 16:26               ` Jens Axboe
2014-02-10 22:41                 ` Kent Overstreet
2014-02-10 23:06                   ` Jens Axboe
2014-02-11  9:12                     ` Christoph Hellwig
2014-02-11 14:42                       ` James Bottomley
2014-02-11 14:53                         ` Christoph Hellwig
2014-02-14 10:36                     ` Alexander Gordeev

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