linux-kernel - Re: [PATCH] scsi: associate bio write hint with WRITE CDB

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Date:   Thu, 10 Jan 2019 17:33:00 +0000
From:   Alex Lemberg <Alex.Lemberg@....com>
To:     "ihhuang@...ail.org" <ihhuang@...ail.org>
CC:     "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "huangrandall@...gle.com" <huangrandall@...gle.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>
Subject: Re: [PATCH] scsi: associate bio write hint with WRITE CDB

Hi Randall,

On Fri, 2019-01-04 at 13:22 +0800, Randall Huang wrote:
> On Thu, Jan 03, 2019 at 11:57:38PM -0500, Martin K. Petersen wrote:
> > 
> > Ewan,
> > 
> > > SBC-5 says that support for the grouping function is indicated by the
> > > GROUP_SUP bit in the Extended Inquiry VPD page (86h).  I'm not sure
> > > how many devices actually support that page though.  Probably most
> > > don't.
> > 
> > Several devices support it, albeit for various different purposes. It's
> > one of these wonderful features whose interpretation was left outside
> > the scope of the spec for a long time.
> > 
> > So even though we absolutely and positively need to make setting GROUP
> > NUMBER conditional on GROUP_SUP being reported, we also need additional
> > information from the storage about how the field should be interpreted.
> > 
> > The official way to report hinting is for the device to implement the IO
> > Advice Hints Grouping mode page. I wrote some code to support that but
> > no vendors that I know of ended up actually shipping an implementation.
> > A few implemented my older I/O class proposal but didn't ship that
> > either despite really convincing performance results.
> > 
> > If Randall has access to a device which implements hinting, I'd love to
> > know more.
> I am working on Android phone.
> The idea is to enable write hint for Turbo write UFS feature.
> Turbo write feature in UFS 3.x is under discussion in JEDEC JC-64. 
> This patch is the under-lying framework for supporting this feature.

As far as I know, there are more than one Turbo Write feature
proposals in JEDEC, which are currently under discussion.
For now, not all proposals are using CDB bytes for enabling
TurboWrite.
So, maybe making this change in SCSI is still too early.

> > 
> > -- 
> > Martin K. Petersen	Oracle Linux Engineering