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Subject: RE: Re: [PATCH v13 0/3] scsi: ufs: Add Host Performance Booster
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Sender: Daejun Park <daejun7.park@samsung.com>
From:   Daejun Park <daejun7.park@samsung.com>
To:     Greg KH <greg@kroah.com>, James Bottomley <jejb@linux.ibm.com>
CC:     Christoph Hellwig <hch@infradead.org>,
        Daejun Park <daejun7.park@samsung.com>,
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        ALIM AKHTAR <alim.akhtar@samsung.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Sang-yoon Oh <sangyoon.oh@samsung.com>,
        Sung-Jun Park <sungjun07.park@samsung.com>,
        yongmyung lee <ymhungry.lee@samsung.com>,
        Jinyoung CHOI <j-young.choi@samsung.com>,
        Adel Choi <adel.choi@samsung.com>,
        BoRam Shin <boram.shin@samsung.com>,
        SEUNGUK SHIN <seunguk.shin@samsung.com>
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Date:   Tue, 08 Dec 2020 13:12:31 +0900
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> > On Mon, 2020-12-07 at 19:35 +0100, Greg KH wrote:
> > > On Mon, Dec 07, 2020 at 06:26:03PM +0000, Christoph Hellwig wrote:
> > > > On Mon, Dec 07, 2020 at 07:23:12PM +0100, Greg KH wrote:
> > > > > What "real workload" test can be run on this to help show if it
> > > > > is useful or not?  These vendors seem to think it helps for some
> > > > > reason, otherwise they wouldn't have added it to their silicon :)
> > > > > 
> > > > > Should they run fio?  If so, any hints on a config that would be
> > > > > good to show any performance increases?
> > > > 
> > > > A real actual workload that matters.  Then again that was Martins
> > > > request to even justify it.  I don't think the broken addressing
> > > > that breaks a whole in the SCSI addressing has absolutely not
> > > > business being supported in Linux ever.  The vendors should have
> > > > thought about the design before committing transistors to something
> > > > that fundamentally does not make sense.
> > 
> > Actually, that's not the way it works: vendors add commands because
> > standards mandate.  That's why people who want weird commands go and
> > join standard committees.  Unfortunately this means that a lot of the
> > commands the standard mandates end up not being very useful in
> > practice.  For instance in SCSI we really only implement a fraction of
> > the commands in the standard.
> > 
> > In this case, the industry already tried a very similar approach with
> > GEN 1 hybrid drives and it turned into a complete disaster, which is
> > why the mode became optional in shingle drives and much better modes,
> > which didn't have the huge shared state problem, superseded it.  Plus
> > truncating the LBA of a READ 16 to 4 bytes is asking for capacity
> > problems down the line, so even the actual implementation seems to be
> > problematic.
> > 
> > All in all, this looks like a short term fix which will go away when
> > the drive capacity improves and thus all the effort changing the driver
> > will eventually be wasted.
> 
> "short term" in the embedded world means "this device is stuck with this
> chip for the next 8 years", it's not like a storage device you can
> replace, so this might be different than the shingle drive mess.  Also,
> I see many old SoCs still showing up in brand new devices many many
> years after they were first introduced, on-chip storage controllers is
> something we need to support well if we don't want to see huge
> out-of-tree patchsets like UFS traditionally has been lugging around for
> many years.
> 
> > > So "time to boot an android system with this enabled and disabled"
> > > would be a valid workload, right?  I'm guessing that's what the
> > > vendors here actually care about, otherwise there is no real stress-
> > > test on a UFS system that I know of.
> > 
> > Um, does it?  I don't believe even the UFS people have claimed this. 
> > The problem is that HPB creates a shared state between the driver and
> > the device.  That shared state has to be populated, which has to happen
> > at start of day, so it's entirely unclear if this is a win or a slow
> > down for boot.
> 
> Ok, showing that this actually matters is a good rule, Daejun, can you
> provide that if you resubmit this patchset?
> 

Sure, I will find out the case which has performance benefit by HPB.

Thanks,
Daejun