linux-kernel - Re: Drivers: scsi

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Message-ID: <1351117520.2494.8.camel@dabdike>
Date:	Thu, 25 Oct 2012 07:25:20 +0900
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	"K. Y. Srinivasan" <kys@...rosoft.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org, ohering@...e.com, hch@...radead.org,
	linux-scsi@...r.kernel.org
Subject: Re: Drivers: scsi

On Wed, 2012-10-24 at 09:25 -0700, K. Y. Srinivasan wrote:
> When the low level driver returns SCSI_MLQUEUE_DEVICE_BUSY,
> how is the command retried; I suspect the retry is done after some delay.

Delay depends mainly on I/O pressure and the unplug timer in the block
layer.

> Is this delay programmable? If the device state changes,
> can the low level driver notify upper layers that it can now handle
> the command that it had failed earlier with SCSI_MLQUEUE_DEVICE_BUSY.

In theory, you can call blk_run_queue() from the event handler that sees
the device become ready.  I don't think any driver actually does this,
but I can't see it would cause any problem.

James


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