RE: [EXT] Re: [PATCH v2 5/5] scsi: ufs: UFS Host Performance Booster(HPB) driver

[Bean Huo (beanhuo)]

Hi, Bart

> 
> What are the similarities and differences compared to the lightnvm framework
> that was added several years ago to the Linux kernel? Which of the code in this
> patch can be shared with the lightnvm framework?
> 
I donât fully comprehend Lightnvm, and studied it in recent days. it is not possible to
deploy Lightnvm framework in UFS HPB. 
UFS HPB has a similar idea with Nvme HMB,  which both take host-side memory as
device onboard flash to hold L2P map entries.  But both are not the same,  UFS HPB
cache cannot be accessed by UFS device over UFS bus. Access and control of UFS HPB
cache completely all depend on the host side UFS HPB driver.
 
HPB has two control modes: device control mode and host control mode.  In the device
Mode, HPB driver reads L2P map data only based on the device recommendations.
However in the host control mode, it is much more flexible, HPB driver completely can
initiate the L2P read actively.  In host mode, HPB can limit read latency and achieve
predictable read latency, since the host side can load the L2P map entries based on its
read behavior and oncoming read. But current exist UFS subsystem, cannot make full
use of this feature.
 
I don't know how do you think about adding a framework in SCSI, let FS can pass oncoming read length to
UFS HPB, the based on that, HPB can load L2P entries in advance.

//Bean