From: Hannes Reinecke <hare@suse.de>
To: Christoph Hellwig <hch@lst.de>,
"Stephen M. Cameron" <scameron@beardog.cce.hp.com>
Cc: james.bottomley@parallels.com, elliott@hp.com,
stephenmcameron@gmail.com, linux-scsi@vger.kernel.org,
Vasu Dev <vasu.dev@linux.intel.com>,
Mike Christie <michaelc@cs.wisc.edu>
Subject: Re: [PATCH] scsi: break from queue depth adjusting loops when device found
Date: Fri, 04 Jul 2014 12:53:00 +0200 [thread overview]
Message-ID: <53B6878C.502@suse.de> (raw)
In-Reply-To: <20140703171106.GA16788@lst.de>
On 07/03/2014 07:11 PM, Christoph Hellwig wrote:
> On Thu, Jul 03, 2014 at 10:05:57AM -0500, Stephen M. Cameron wrote:
>> From: Stephen M. Cameron <scameron@beardog.cce.hp.com>
>>
>> Don't loop through all the devices even after
>> finding the one we're looking for
>
> The comments in the code seem to indicate that we want to modify
> the queue depth for all LUNs on a given target.
>
> Ccing Mike and Vasu as they wrote this code.
>
Indeed, that was the idea.
This piece of code tries to keep track of the remote port queue
depth, which isn't represented at all.
Thing is, each remote target has a target queue depth which can hold
only so many outstanding SCSI requests. If that is full it'll return
BUSY for _all_ LUNs served from that port.
And the very _next_ command after the one which filled the target
queue will get the BUSY status.
So we need to decrease the queue depth on _all_ LUNs here to avoid
starvation of individual devices.
Hence I guess this is not the correct fix.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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next prev parent reply other threads:[~2014-07-04 10:53 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-03 15:05 [PATCH] scsi: break from queue depth adjusting loops when device found Stephen M. Cameron
2014-07-03 15:25 ` Douglas Gilbert
2014-07-03 17:11 ` Christoph Hellwig
2014-07-03 17:21 ` Mike Christie
2014-07-04 18:36 ` Douglas Gilbert
2014-07-04 10:53 ` Hannes Reinecke [this message]
2014-07-04 19:21 ` Elliott, Robert (Server Storage)
2014-07-06 9:49 ` Christoph Hellwig
2014-07-26 15:36 ` Christoph Hellwig
[not found] ` <CADzpL0Rn+x6N=v123EBej_iZhTwmjMYZ4deeTeRG7_sxgXU9PQ@mail.gmail.com>
2014-07-26 16:17 ` Christoph Hellwig
2014-07-27 15:36 ` Hannes Reinecke
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