[RFC PATCH 0/5] scsi: ufs: Add Host Performance Booster Support

[Daejun Park]

NAND flash memory-based storage devices use Flash Translation Layer (FTL)
to translate logical addresses of I/O requests to corresponding flash
memory addresses. Mobile storage devices typically have RAM with
constrained size, thus lack in memory to keep the whole mapping table.
Therefore, mapping tables are partially retrieved from NAND flash on
demand, causing random-read performance degradation.

To improve random read performance, we propose HPB (Host Performance
Booster) which uses host system memory as a cache for the FTL mapping
table. By using HPB, FTL data can be read from host memory faster than from
NAND flash memory. 

The current version only supports the DCM (device control mode).
This patch consists of 4 parts to support HPB feature.

1) UFS-feature layer
2) HPB probe and initialization process
3) READ -> HPB READ using cached map information
4) L2P (logical to physical) map management

The UFS-feature is an additional layer to avoid the structure in which the
UFS-core driver and the UFS-feature are entangled with each other in a 
single module.
By adding the layer, UFS-features composed of various combinations can be
supported. Also, even if a new feature is added, modification of the 
UFS-core driver can be minimized.

In the HPB probe and init process, the device information of the UFS is
queried. After checking supported features, the data structure for the HPB
is initialized according to the device information.

A read I/O in the active sub-region where the map is cached is changed to
HPB READ by the HPB module.

The HPB module manages the L2P map using information received from the
device. For active sub-region, the HPB module caches through ufshpb_map
request. For the in-active region, the HPB module discards the L2P map.
When a write I/O occurs in an active sub-region area, associated dirty
bitmap checked as dirty for preventing stale read.

HPB is shown to have a performance improvement of 58 - 67% for random read
workload. [1]

This series patches are based on the "5.8/scsi-queue" branch.

[1]:
https://www.usenix.org/conference/hotstorage17/program/presentation/jeong

Daejun park (5):
 scsi: ufs: Add UFS feature related parameter
 scsi: ufs: Add UFS feature layer
 scsi: ufs: Introduce HPB module
 scsi: ufs: L2P map management for HPB read
 scsi: ufs: Prepare HPB read for cached sub-region
 
 drivers/scsi/ufs/Kconfig      |    8 +
 drivers/scsi/ufs/Makefile     |    3 +-
 drivers/scsi/ufs/ufs.h        |   11 +
 drivers/scsi/ufs/ufsfeature.c |  178 ++++
 drivers/scsi/ufs/ufsfeature.h |   95 ++
 drivers/scsi/ufs/ufshcd.c     |   19 +
 drivers/scsi/ufs/ufshcd.h     |    3 +
 drivers/scsi/ufs/ufshpb.c     | 2029 +++++++++++++++++++++++++++++++++++++++++
 drivers/scsi/ufs/ufshpb.h     |  257 ++++++
 9 files changed, 2602 insertions(+), 1 deletion(-)
 created mode 100644 drivers/scsi/ufs/ufsfeature.c
 created mode 100644 drivers/scsi/ufs/ufsfeature.h
 created mode 100644 drivers/scsi/ufs/ufshpb.c
 created mode 100644 drivers/scsi/ufs/ufshpb.h