Re: [PATCH 1/6] libata: Do not retry commands with valid autosense

[Hannes Reinecke <hare@suse.de>]

On 08/02/2015 05:44 PM, Tejun Heo wrote:
> Hello,
> 
> On Fri, Jul 31, 2015 at 03:02:03PM +0200, Hannes Reinecke wrote:
>> If a failed command has a valid autosense there is no need to
>> retry it on the ATA level; at best we're incurring the same
>> error again. So rather not retry it here, but leave it to
>> the SCSI layer to decide if a retry is in order.
> 
> Hmmm... I don't know.  So, we change how we handle errors completely
> depending on how the device reports it?  Doesn't seem like a
> particularly good idea to me.
> 
The whole point of the autosense feature is that you do _not_
have to fall back to the original trial-and-error libata EH,
but know exactly what the problem is. Plus any retry will be giving
us (in most cases) exactly the same sense code.
_And_ the SCSI layer is actually able to understand the sense code,
allowing him to make a better judgment on what to do with that error.

So any retry in the libata layer will only slow things down,
leading to the same results eventually.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
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