linux-ext4 - Re: [PATCH] ext4: fix lazyinit thread prevent from sleep

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Message-ID: <20101025144634.GD16981@thunk.org>
Date:	Mon, 25 Oct 2010 10:46:34 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org, sandeen@...hat.com
Subject: Re: [PATCH] ext4: fix lazyinit thread prevent from sleep

On Fri, Oct 22, 2010 at 08:57:45PM +0200, Lukas Czerner wrote:
> In my test lazyinit threat (in linux-next tree) consumes too much CPU
> (90%). The reason is that there is a bug preventing the threat to sleep
> and hence it keeps walking the li_request_list until the time for next
> scheduled request comes.
> 
> It is because the next_wakeup is originally set to jiffies - 1 so the
> thread is assuming that there is no reason to sleep, because the time
> for next scheduled event is already came, however that is not true.
> 
> I have fixed that by setting next_wakeup to MAX_JIFFY_OFFSET initially
> and than setting value of the next scheduled request (the one with the
> smallest lr_next_sched value). It has been tested and now the CPU
> utilization of lazyinit thread is under 1% (with one request in the list).
> 
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>

Thanks, I've merged this into the lazy-init patch in the ext4 patch queue.

	     	    	      	  	    	  - Ted
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