Re: [PATCH] mmc: block: Support Host to control FUA.

[Chaitanya Kulkarni]

On 10/19/22 19:45, Wenchao Chen wrote:
> From: Wenchao Chen <wenchao.chen@xxxxxxxxxx>
> 
> This patch introduces host->fua_disable for MMC host controller.
> The host can turn off FUA to improve performance.
> 
> 1. fua_disable = 1
> /sys/block/mmcblk0/queue # cat fua 0
> I tested 5 times for each case and output a average speed.
> 
> 1) Sequential read:
> Speed: 266.8MiB/s, 265.1MiB/s, 262.9MiB/s, 268.7MiB/s, 265.2MiB/s
> Average speed: 265.74MiB/s
> 
> 2) Random read:
> Speed: 98.75MiB/s, 98.7MiB/s, 98.5MiB/s, 99.4MiB/s, 98.7MiB/s
> Average speed: 98.81MiB/s
> 
> 3) Sequential write:
> Speed: 199.94MiB/s, 199.1MiB/s, 205.5MiB/s, 206.5MiB/s, 191.5MiB/s
> Average speed: 200.5MiB/s
> 
> 4) Random write:
> Speed: 68.6MiB/s, 71.8MiB/s, 77.1MiB/s, 64.8MiB/s, 69.3MiB/s
> Average speed: 70.32MiB/s
> 
> 2. fua_disable = 0 (default 0)
> /sys/block/mmcblk0/queue # cat fua 1
> I tested 5 times for each case and output a average speed.
> 
> 1) Sequential read:
> Speed: 259.3MiB/s, 258.8MiB/s, 258.2MiB/s, 259.5MiB/s, 253.5MiB/s
> Average speed: 257.86MiB/s
> 
> 2) Random read:
> Speed: 98.9MiB/s, 101MiB/s, 101MiB/s, 99MiB/s, 101.1MiB/s
> Average speed: 100.2MiB/s
> 
> 3) Sequential write:
> Speed: 153.7MiB/s, 146.2MiB/s, 151.2MiB/s, 148.8MiB/s, 147.5MiB/s
> Average speed: 149.48MiB/s
> 
> 4) Random write:
> Speed: 12.9MiB/s, 12.3MiB/s, 12.6MiB/s, 12.8MiB/s, 12.8MiB/s
> Average speed: 12.68MiB/s
> 
> According to the above data, disable FUA (fua_disable = 1) improves the
> performance. Therefore, it is recommended to support the host to control
> FUA.
> 
> Signed-off-by: Wenchao Chen <wenchao.chen@xxxxxxxxxx>

Based on the data provided seems it does increase the performance.
Perhaps it is worth mentioning the reason behind the performance
increase and other side effects of doing so ?

Also, it is usually helpful to mention performance increase in the
% in the commit log so you can move verbose log (like above) into
the cover-letter for documentation purpose, this is based on
the feedback I got, unless maintainer(s) prefers is this way :).

-ck