Re: [PATCH 0/4] New SCSI command timeout handler

[Hannes Reinecke <hare@suse.de>]

On 06/07/2013 08:54 AM, Ren Mingxin wrote:
> Hi, Hannes:
> 
> On 06/06/2013 05:43 PM, Hannes Reinecke wrote:
>> this is the first step towards a new non-blocking
>> error handler. This patch implements a new command
>> timeout handler which will be sending command aborts
>> inline without engaging SCSI EH.
>>
>> In addition the commands will be returned directly
>> if the command abort succeeded, cutting down recovery
>> times dramatically.
>>
>> With the original scsi error recovery I got:
>> # time dd if=/dev/zero of=/mnt/test.blk bs=512 count=2048 oflag=sync
>> 2048+0 records in
>> 2048+0 records out
>> 1048576 bytes (1.0 MB) copied, 3.72732 s, 281 kB/s
>>
>> real    2m14.475s
>> user    0m0.000s
>> sys    0m0.104s
>>
>> with this patchset I got:
>> # time dd if=/dev/zero of=/mnt/test.blk bs=512 count=2048 oflag=sync
>> 2048+0 records in
>> 2048+0 records out
>> 1048576 bytes (1.0 MB) copied, 31.5151 s, 33.3 kB/s
>>
>> real    0m31.519s
>> user    0m0.000s
>> sys    0m0.088s
>>
>> Test was to disable RSCN on the target port, disable the
>> target port, and then start the 'dd' command as indicated.
>>
>> As a proof-of-concept I've also enabled the new timeout
>> handler for virtio, so that things can be tested out
>> more easily.
> 
> So this 31.5s is tested on virtio disks, right? Much faster than your
> former test via fc.
> 
No. This was done on HP Proliant /QLogic FC running against HP P2000.

There is a reason why I posted this new patchset :-)

(The old patchset had a bug where it wouldn't abort the TUR send by
multipaths path-checker. Which were causing delays during
switchover. This version now does terminate them properly)
(Incidentally, it was the non-working scsi_noretry_cmd() which
caused this bug :-)

> This approach may not work for some LLDDs as you said, but I wonder
> whether SAS is applicable(whether there will be later patches for
> SAS).
> 
SAS should be applicable for this, too. I'll check.

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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