RE: [PATCH V2 0/2] mmc: block: Support Host to control FUA

[Avri Altman]

> 
> From: Wenchao Chen <wenchao.chen@xxxxxxxxxx>
> 
> Summary
> =======
> These patches[1] supports the host to turn off FUA.
> 
> About FUA, roughly deal with the following two parts:
> 1) FUA(Forced Unit Access):
> - The REQ_FUA flag can be OR ed into the r/w flags of a bio submitted from the
>   filesystem and will make sure that I/O completion for this request is only
>   signaled after the data has been committed to non-volatile storage.
> 
> 2) In emmc, FUA is represented as Reliable write. code show as below:
> static void mmc_blk_data_prep(struct mmc_queue *mq, struct mmc_queue_req
> *mqrq,
>                 int recovery_mode, bool *do_rel_wr_p, bool *do_data_tag_p) {
>         ...
>         /*
>          * Reliable writes are used to implement Forced Unit Access and
>          * are supported only on MMCs.
>          */
>         do_rel_wr = (req->cmd_flags & REQ_FUA) &&
>                         rq_data_dir(req) == WRITE &&
>                         (md->flags & MMC_BLK_REL_WR);
>         ...
> }
> 
> Patch structure
> ===============
> patch#1:  for block
> patch#2:  for sdhci-sprd
> 
> Tests
> =====
> Ran 'AndroBench' to evaluate the 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:
> 1)Sequential read improved by 3%.
> 2)Random read were down 1%.
> 3)Sequential write improved by 34%.
> 4)Random write improved by 454%.
> Therefore, it is recommended to support the host to control FUA.
> 
> Reference
> =========
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Docume
> ntation/block/writeback_cache_control.rst
> [2] Embedded Multi-Media Card (e•MMC) Electrical Standard (5.1)''
> 
> Wenchao Chen (2):
>   mmc: block: Support Host to control FUA
>   mmc: sdhci-sprd: enable fua_disable for SPRDSDHCI

Reviewed-by: Avri Altman <avri.altman@xxxxxxx>

> 
>  drivers/mmc/core/block.c      | 3 ++-
>  drivers/mmc/host/sdhci-sprd.c | 2 ++
>  include/linux/mmc/host.h      | 3 +++
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> --
> 2.17.1