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

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Date:   Fri, 4 Jan 2019 13:22:51 +0800
From:   Randall Huang <ihhuang@...ail.org>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     jejb@...ux.vnet.ibm.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, huangrandall@...gle.com
Subject: Re: [PATCH] scsi: associate bio write hint with WRITE CDB

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