linux-kernel - Re: [RESENT PATCH RFC v3 5/5] scsi: ufs: UFS Host Performance Booster(HPB) driver

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Date:   Fri, 08 May 2020 12:08:03 +0200
From:   Bean Huo <huobean@...il.com>
To:     Randy Dunlap <rdunlap@...radead.org>, alim.akhtar@...sung.com,
        avri.altman@....com, asutoshd@...eaurora.org, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, stanley.chu@...iatek.com,
        beanhuo@...ron.com, bvanassche@....org, tomas.winkler@...el.com,
        hch@...radead.org
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        cang@...eaurora.org
Subject: Re: [RESENT PATCH RFC v3 5/5] scsi: ufs: UFS Host Performance
 Booster(HPB) driver

On Thu, 2020-05-07 at 18:34 -0700, Randy Dunlap wrote:
> Hi,
> 
> On 5/4/20 7:20 AM, huobean@...il.com wrote:
> > diff --git a/drivers/scsi/ufs/Kconfig b/drivers/scsi/ufs/Kconfig
> > index e2005aeddc2d..0224f224a641 100644
> > --- a/drivers/scsi/ufs/Kconfig
> > +++ b/drivers/scsi/ufs/Kconfig
> > @@ -160,3 +160,65 @@ config SCSI_UFS_BSG
> >  
> >  	  Select this if you need a bsg device node for your UFS
> > controller.
> >  	  If unsure, say N.
> > +
> > +config SCSI_UFSHPB
> > +	bool "UFS Host Performance Booster (EXPERIMENTAL)"
> > +	depends on SCSI_UFSHCD
> > +	help
> > +	  NAND flash-based storage devices, including UFS, have
> > mechanisms to
> > +	  translate logical addresses of the IO requests to the
> > corresponding
> > +	  physical addresses of the flash storage. Traditionally, this
> > L2P
> > +	  mapping data is loaded to the internal SRAM in the storage
> > controller.
> > +	  When the capacity of storage is larger, a larger size of SRAM
> > for the
> > +	  L2P map data is required. Since increased SRAM size affects
> > the
> > +	  manufacturing cost significantly, it is not cost-effective to
> > allocate
> > +	  all the amount of SRAM needed to keep all the Logical-address 
> > to
> > +	  Physical-address (L2P) map data. Therefore, L2P map data,
> > which is
> > +	  required to identify the physical address for the requested
> > IOs, can
> > +	  only be partially stored in SRAM from NAND flash. Due to this
> > partial
> > +	  loading, accessing the flash address area where the L2P
> > information
> > +	  for that address is not loaded in the SRAM can result in
> > serious
> > +	  performance degradation.
> > +
> > +	  UFS Host Performance Booster (HPB) is a software solution for
> > the
> > +	  above problem, which uses the host side system memory as a
> > cache for
> > +	  the FTL L2P mapping table. It does not need additional
> > hardware
> > +	  support from the host side. By using HPB, the L2P mapping
> > table can be
> > +	  read from host memory and stored in host-side memory. when
> > performing
> 
> Should that be: from device memory and stored in host-side memory.
> ?
> 
> Also, s/when/When/
> 
> 
> > +	  the read operation, the corresponding L2P information will be
> > sent to
> > +	  the UFS device along with the reading request. Since the L2P
> > entry is
> 
> s/reading/read/
> 
> > +	  provided in the read request, UFS device does not have to
> > load L2P
> > +	  entry from flash memory to UFS internal SRAM. This will
> > significantly
> > +	  improve the read performance.
> > +
> > +	  When selected, this feature will be built in the UFS driver.
> > +
> > +	  If in doubt, say N.
> > +
> > +config UFSHPB_MAX_MEM_SIZE
> > +	int "UFS HPB maximum memory size per controller (in MiB)"
> > +	depends on SCSI_UFSHPB
> > +	default 128
> > +	range 0 65536
> > +	help
> > +	  This parameter defines the maximum UFS HPB memory/cache size
> > in the
> > +	  host system. The recommended HPB cache size by the UFS device
> > can be
> > +	  calculated from bHPBRegionSize and
> > wDeviceMaxActiveHPBRegions. The
> > +	  reference formula can be
> 
> s/can be/is/
> 
> > +
> > +		(bHPBRegionSize(in KB) / 4KB) * 8 *
> > wDeviceMaxActiveHPBRegions.
> > +
> > +	  The HPB cache in the host system is used to contain L2P
> > mapping
> > +	  entries. If the allocated HPB cache size is lower than what
> > calculated
> 
> 	                                                    than that
> 
> > +	  by the above formula, the use of HPB feature may provide
> > lower
> > +	  performance advantage. But the system memory resource has the
> > +	  limitation, we can not let HPB driver allocate its cache at
> > will
> > +	  according to the UFS device recommendation, so an appropriate
> > size of
> > +	  the cache for HPB should be specified before you choose to
> > use HPB,
> > +	  then please enter a non-zero positive integer value.
> > +
> > +	  Nevertheless, if you want to leave this to the HPB driver,
> > and let the
> > +	  HPB driver allocate the HPB cache based on the recommendation
> > of the
> > +	  UFS device. Just give 0 value to this parameter.
> > +
> > +	  Leave the default value if unsure.
> 
> thanks.


Hi Randy
Thanks for your review. I will change them based on your
comments.

thanks,

Bean