Re: Drivers: scsi: FLUSH timeout

[Mike Christie <michaelc@cs.wisc.edu>]

On 09/24/2013 07:35 AM, KY Srinivasan wrote:
> 
> 
>> -----Original Message-----
>> From: Jack Wang [mailto:xjtuwjp@gmail.com]
>> Sent: Tuesday, September 24, 2013 5:08 AM
>> To: KY Srinivasan
>> Cc: Greg KH; linux-kernel@vger.kernel.org; devel@linuxdriverproject.org;
>> ohering@suse.com; jbottomley@parallels.com; hch@infradead.org; linux-
>> scsi@vger.kernel.org; Mike Christie
>> Subject: Re: Drivers: scsi: FLUSH timeout
>>
>> On 09/21/2013 07:24 AM, KY Srinivasan wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Greg KH [mailto:gregkh@linuxfoundation.org]
>>>> Sent: Friday, September 20, 2013 1:32 PM
>>>> To: KY Srinivasan
>>>> Cc: linux-kernel@vger.kernel.org; devel@linuxdriverproject.org;
>>>> ohering@suse.com; jbottomley@parallels.com; hch@infradead.org; linux-
>>>> scsi@vger.kernel.org
>>>> Subject: Re: Drivers: scsi: FLUSH timeout
>>>>
>>>> On Fri, Sep 20, 2013 at 12:32:27PM -0700, K. Y. Srinivasan wrote:
>>>>> The SD_FLUSH_TIMEOUT value is currently hardcoded.
>>>>
>>>> Hardcoded where?  Please, more context.
>>>
>>> This is defined in scsi/sd.h:
>>>
>>> #define SD_FLUSH_TIMEOUT        (60 * HZ)
>>>>
>>>>> On our cloud, we sometimes hit this timeout. I was wondering if we
>>>>> could make this a module parameter. If this is acceptable, I can send
>>>>> you a patch for this.
>>>>
>>>> A module parameter don't make sense for a per-device value, does it?
>>> Currently, the 60 second timeout is applied across devices. Ideally, I want to be
>>> able to control the FLUSH TIMEOUT as we currently do I/O timeout. If this is
>>> acceptable, I can work on a patch for that as well.
>>>
>>> Regards,
>>>
>>> K. Y
>>>>
>>>> greg k-h
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>> Hi,
>>
>> Back to 2010, Mike(cc-ed) try to add a flush time out interface, similar
>> to what you want here, no idea why it's just ignored?
>> http://www.spinics.net/lists/linux-scsi/msg45017.html
> 
> Thanks Jack. Mike, do you know what the concerns were as to why this
> patch was not accepted?
> 

I do not remember the exact concerns. We ended up just increasing the
hard coded value in:

commit e3b3e6246726cd05950677ed843010b8e8c5884c
Author: Mike Christie <mchristi@redhat.com>
Date:   Wed Aug 11 11:06:25 2010 -0500

    [SCSI] scsi/block: increase flush/sync timeout


In the git commit message there is a comment about people thinking
making it configurable for users was troublesome.