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

[Wenchao Chen]

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/Documentation/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

 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