On 6 November 2015 at 16:12, Luca Porzio (lporzio) <lpor...@micron.com> wrote:
> mmc: remove bondage between REQ_META and reliable write
>
> Anytime a write operation is performed with Reliable Write flag enabled,
> the eMMC device is enforced to bypass the cache and do a write to the
> underling NVM device by Jedec specification; this causes a performance
> penalty since write operations cannot be optimized by the device cache.
>
> In our tests, we replayed a typical mobile daily trace pattern and
> found ~9% overall time reduction in trace replay by using this patch.
> Also the write ops within 4KB~64KB chunk size range get a 40~60%
> performance improvement by using the patch (as this range of write
> chunks are the one affected by REQ_META).
>
> This patch has been discussed in the Mobile & Embedded Linux Storage
> Forum and it is the results of feedbacks from many people.
> We also checked with fsdevl and f2fs mailing list developers that this change
> in the usage of REQ_META is not affecting FS behavior and we got
> positive feedbacks on applying this patch.
> Reporting here the feedbacks:
> - http://comments.gmane.org/gmane.linux.file-systems/97219
> - http://thread.gmane.org/gmane.linux.file-systems.f2fs/3178/focus=3183
>
> Signed-off-by: Bruce Ford <bf...@micron.com>
> Signed-off-by: Luca Porzio <lpor...@micron.com>
I browsed the history to understand when the behaviour of REQ_META was
introduced. It's really strange as it seems to slipped through when
"packed command" support was added [1].
I couldn't find any related information to why, so probably it was
just a mistake. For that reason, I decided to add a fixes tag to the
commit message for $subject patch.
Moreover, I also updated minor parts in the change log to silence some
checkpatch warnings.
Applied for fixes, thanks!
Kind regards
Uffe
[1]
commit ce39f9d17c14e56ea6772aa84393e6e0cc8499c4
Author: Seungwon Jeon <tgih....@samsung.com>
Date: Wed Feb 6 17:02:46 2013 +0900
mmc: support packed write command for eMMC4.5 devices
> ---
> drivers/mmc/card/block.c | 11 +++--------
> 1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index 4409d79..cba6d5e 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -62,8 +62,7 @@ MODULE_ALIAS("mmc:block");
> #define MMC_SANITIZE_REQ_TIMEOUT 240000
> #define MMC_EXTRACT_INDEX_FROM_ARG(x) ((x & 0x00FF0000) >> 16)
>
> -#define mmc_req_rel_wr(req) (((req->cmd_flags & REQ_FUA) || \
> - (req->cmd_flags & REQ_META)) && \
> +#define mmc_req_rel_wr(req) ((req->cmd_flags & REQ_FUA) && \
> (rq_data_dir(req) == WRITE))
> #define PACKED_CMD_VER 0x01
> #define PACKED_CMD_WR 0x02
> @@ -1353,13 +1352,9 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req
> *mqrq,
>
> /*
> * Reliable writes are used to implement Forced Unit Access and
> - * REQ_META accesses, and are supported only on MMCs.
> - *
> - * XXX: this really needs a good explanation of why REQ_META
> - * is treated special.
> + * are supported only on MMCs.
> */
> - bool do_rel_wr = ((req->cmd_flags & REQ_FUA) ||
> - (req->cmd_flags & REQ_META)) &&
> + bool do_rel_wr = (req->cmd_flags & REQ_FUA) &&
> (rq_data_dir(req) == WRITE) &&
> (md->flags & MMC_BLK_REL_WR);
>
> --
> 2.1.1
>
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