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Subject: Re: [RESENT PATCH RFC v3 5/5] scsi: ufs: UFS Host Performance
 Booster(HPB) driver
To:     huobean@gmail.com, alim.akhtar@samsung.com, avri.altman@wdc.com,
        asutoshd@codeaurora.org, jejb@linux.ibm.com,
        martin.petersen@oracle.com, stanley.chu@mediatek.com,
        beanhuo@micron.com, bvanassche@acm.org, tomas.winkler@intel.com,
        cang@codeaurora.org
Cc:     linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        hch@infradead.org
References: <20200504142032.16619-1-beanhuo@micron.com>
 <20200504142032.16619-6-beanhuo@micron.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <38db2ee7-18ff-9263-1cc7-1b9c6f085632@infradead.org>
Date:   Thu, 7 May 2020 18:34:02 -0700
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Hi,

On 5/4/20 7:20 AM, huobean@gmail.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.
-- 
~Randy