23646f0134
Avri Altman <avri.altman@wdc.com> says: The rtt-upiu packets precede any data-out upiu packets, thus synchronizing the data input to the device: this mostly applies to write operations, but there are other operations that requires rtt as well. There are several rules binding this rtt - data-out dialog, specifically There can be at most outstanding bMaxNumOfRTT such packets. This might have an effect on write performance (sequential write in particular), as each data-out upiu must wait for its rtt sibling. UFSHCI expects bMaxNumOfRTT to be min(bDeviceRTTCap, NORTT). However, as of today, there does not appear to be no-one who sets it: not the host controller nor the driver. It wasn't an issue up to now: bMaxNumOfRTT is set to 2 after manufacturing, and wasn't limiting the write performance. UFS4.0, and specifically gear 5 changes this, and requires the device to be more attentive. This doesn't come free - the device has to allocate more resources to that end, but the sequential write performance improvement is significant. Early measurements shows 25% gain when moving from rtt 2 to 9. Therefore, set bMaxNumOfRTT to be min(bDeviceRTTCap, NORTT) as UFSHCI expects. Link: https://lore.kernel.org/r/20240530142510.734-1-avri.altman@wdc.com Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.