On 6 November 2015 at 16:12, Luca Porzio (lporzio) <lporzio@xxxxxxxxxx> 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 <bford@xxxxxxxxxx> > Signed-off-by: Luca Porzio <lporzio@xxxxxxxxxx> 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.jun@xxxxxxxxxxx> 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
