From: KY Srinivasan <kys@microsoft.com>
To: Mike Christie <michaelc@cs.wisc.edu>
CC: Jack Wang <xjtuwjp@gmail.com>, Greg KH <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "ohering@suse.com" <ohering@suse.com>,
        "jbottomley@parallels.com" <jbottomley@parallels.com>,
        "hch@infradead.org" <hch@infradead.org>,
        "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>
Subject: RE: Drivers: scsi: FLUSH timeout
Thread-Topic: Drivers: scsi: FLUSH timeout
Thread-Index: AQHOtkBtWGcmfS/7wkmW+8Ppp9OK8pnPmBJggAU49YCAAAdE0IAAT/uAgABKyIA=
Date: Tue, 24 Sep 2013 21:53:00 +0000
Message-ID: <bf168ab724a140f989ab3dfe877b750f@SN2PR03MB061.namprd03.prod.outlook.com>
References: <1379705547-15028-1-git-send-email-kys@microsoft.com>
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 <3413dbd7fa254fd380a84fe6d9cd87e1@SN2PR03MB061.namprd03.prod.outlook.com>
 <5241C9E7.2000404@cs.wisc.edu>
In-Reply-To: <5241C9E7.2000404@cs.wisc.edu>
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> -----Original Message-----
> From: Mike Christie [mailto:michaelc@cs.wisc.edu]
> Sent: Tuesday, September 24, 2013 10:21 AM
> To: KY Srinivasan
> Cc: Jack Wang; Greg KH; 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 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
> >>> --
> >>> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> >>> the body of a message to majordomo@vger.kernel.org
> >>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>>
> >> 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.

I am not sure how that magic number was arrived at (the 60HZ number). We want this to be little higher -
would there be any issues raising this to say  180 seconds. This is the value we currently have for I/O
timeout.

Regards,

K. Y

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