linux-kernel - Re: Prevent busy looping

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Message-ID: <484F86D4.8050907@gmail.com>
Date:	Wed, 11 Jun 2008 17:03:32 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Jens Axboe <jens.axboe@...cle.com>, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Prevent busy looping

Alan Cox wrote:
>> Elias's synthetic test case triggered infinite loop because it wasn't
>> a proper ->qc_defer().  ->qc_defer() should never defer commands when
>> the target is idle.
> 
> Target or host ? We *do* defer commands in the case of an idle channel
> when dealing with certain simplex controllers that can only issue one
> command per host not one per cable (and in fact in the general case we
> can defer commands due to activity on the other drive on the cable).

The term was confusing.  I used target to mean both device
(ATA_DEFER_LINK) and host (ATA_DEFER_PORT).  Hmmm... in simplex case,
yeah, blocked counters need to be > 1.  We'll need to increase blocked
counts after all.  I'll test blocked counts of 2 w/ PMP and make sure it
doesn't incur unnecessary delays and post the patch.

Thanks.

-- 
tejun
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