RE: [PATCH v2 1/1] mmc: block: Add write packing control

[Seungwon Jeon <tgih.jun@samsung.com>]

Hi,

How can we check the effect?
Do you have any result?
Please check the several comment below.

Maya Erez <merez@codeaurora.org> wrote:
> The write packing control will ensure that read requests latency is
> not increased due to long write packed commands.
> 
> The trigger for enabling the write packing is managing to pack several
> write requests. The number of potential packed requests that will trigger
> the packing can be configured via sysfs by writing the required value to:
> /sys/block/<block_dev_name>/num_wr_reqs_to_start_packing.
> The trigger for disabling the write packing is fetching a read request.
> 
> ---
>  Documentation/mmc/mmc-dev-attrs.txt |   17 ++++++
>  drivers/mmc/card/block.c            |  100 ++++++++++++++++++++++++++++++++++-
>  drivers/mmc/card/queue.c            |    8 +++
>  drivers/mmc/card/queue.h            |    3 +
>  include/linux/mmc/host.h            |    1 +
>  5 files changed, 128 insertions(+), 1 deletions(-)
> 
> diff --git a/Documentation/mmc/mmc-dev-attrs.txt b/Documentation/mmc/mmc-dev-attrs.txt
> index 22ae844..08f7312 100644
> --- a/Documentation/mmc/mmc-dev-attrs.txt
> +++ b/Documentation/mmc/mmc-dev-attrs.txt
> @@ -8,6 +8,23 @@ The following attributes are read/write.
> 
>  	force_ro		Enforce read-only access even if write protect switch is off.
> 
> +	num_wr_reqs_to_start_packing 	This attribute is used to determine
> +	the trigger for activating the write packing, in case the write
> +	packing control feature is enabled.
> +
> +	When the MMC manages to reach a point where num_wr_reqs_to_start_packing
> +	write requests could be packed, it enables the write packing feature.
> +	This allows us to start the write packing only when it is beneficial
> +	and has minimum affect on the read latency.
> +
> +	The number of potential packed requests that will trigger the packing
> +	can be configured via sysfs by writing the required value to:
> +	/sys/block/<block_dev_name>/num_wr_reqs_to_start_packing.
> +
> +	The default value of num_wr_reqs_to_start_packing was determined by
> +	running parallel lmdd write and lmdd read operations and calculating
> +	the max number of packed writes requests.
> +
>  SD and MMC Device Attributes
>  ============================
> 
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index 2785fd4..ef192fb 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -114,6 +114,7 @@ struct mmc_blk_data {
>  	struct device_attribute force_ro;
>  	struct device_attribute power_ro_lock;
>  	int	area_type;
> +	struct device_attribute num_wr_reqs_to_start_packing;
>  };
> 
>  static DEFINE_MUTEX(open_lock);
> @@ -281,6 +282,38 @@ out:
>  	return ret;
>  }
> 
> +static ssize_t
> +num_wr_reqs_to_start_packing_show(struct device *dev,
> +				  struct device_attribute *attr, char *buf)
> +{
> +	struct mmc_blk_data *md = mmc_blk_get(dev_to_disk(dev));
> +	int num_wr_reqs_to_start_packing;
> +	int ret;
> +
> +	num_wr_reqs_to_start_packing = md->queue.num_wr_reqs_to_start_packing;
> +
> +	ret = snprintf(buf, PAGE_SIZE, "%d\n", num_wr_reqs_to_start_packing);
> +
> +	mmc_blk_put(md);
> +	return ret;
> +}
> +
> +static ssize_t
> +num_wr_reqs_to_start_packing_store(struct device *dev,
> +				 struct device_attribute *attr,
> +				 const char *buf, size_t count)
> +{
> +	int value;
> +	struct mmc_blk_data *md = mmc_blk_get(dev_to_disk(dev));
> +
> +	sscanf(buf, "%d", &value);
> +	if (value >= 0)
> +		md->queue.num_wr_reqs_to_start_packing = value;
> +
> +	mmc_blk_put(md);
> +	return count;
> +}
> +
>  static int mmc_blk_open(struct block_device *bdev, fmode_t mode)
>  {
>  	struct mmc_blk_data *md = mmc_blk_get(bdev->bd_disk);
> @@ -1313,6 +1346,48 @@ static void mmc_blk_rw_rq_prep(struct mmc_queue_req *mqrq,
>  	mmc_queue_bounce_pre(mqrq);
>  }
> 
> +static void mmc_blk_write_packing_control(struct mmc_queue *mq,
> +					  struct request *req)
> +{
> +	struct mmc_host *host = mq->card->host;
> +	int data_dir;
> +
> +	if (!(host->caps2 & MMC_CAP2_PACKED_WR))
> +		return;
> +
> +	/*
> +	 * In case the packing control is not supported by the host, it should
> +	 * not have an effect on the write packing. Therefore we have to enable
> +	 * the write packing
> +	 */
> +	if (!(host->caps2 & MMC_CAP2_PACKED_WR_CONTROL)) {
> +		mq->wr_packing_enabled = true;
> +		return;
> +	}
> +
> +	if (!req || (req && (req->cmd_flags & REQ_FLUSH))) {
> +		if (mq->num_of_potential_packed_wr_reqs >
> +				mq->num_wr_reqs_to_start_packing)
> +			mq->wr_packing_enabled = true;
> +		return;
> +	}
> +
> +	data_dir = rq_data_dir(req);
> +
> +	if (data_dir == READ) {
> +		mq->num_of_potential_packed_wr_reqs = 0;
> +		mq->wr_packing_enabled = false;
> +		return;
> +	} else if (data_dir == WRITE) {
> +		mq->num_of_potential_packed_wr_reqs++;
> +	}
> +
> +	if (mq->num_of_potential_packed_wr_reqs >
> +			mq->num_wr_reqs_to_start_packing)
> +		mq->wr_packing_enabled = true;
Write Packing is available only if continuing write requests are over num_wr_reqs_to_start_packing?
That means individual request(1...17) will be issued with non-packing.
Could you explain your policy more?
> +
> +}
> +
>  static u8 mmc_blk_prep_packed_list(struct mmc_queue *mq, struct request *req)
>  {
>  	struct request_queue *q = mq->queue;
> @@ -1332,6 +1407,9 @@ static u8 mmc_blk_prep_packed_list(struct mmc_queue *mq, struct request *req)
>  			!card->ext_csd.packed_event_en)
>  		goto no_packed;
> 
> +	if (!mq->wr_packing_enabled)
> +		goto no_packed;
If wr_packing_enabled is set to true, several write requests can be packed.
We don't need to consider read request since packed write?

Thanks,
Seungwon Jeon
> +
>  	if ((rq_data_dir(cur) == WRITE) &&
>  			(card->host->caps2 & MMC_CAP2_PACKED_WR))
>  		max_packed_rw = card->ext_csd.max_packed_writes;
> @@ -1396,6 +1474,8 @@ static u8 mmc_blk_prep_packed_list(struct mmc_queue *mq, struct request *req)
>  			break;
>  		}
> 
> +		if (rq_data_dir(next) == WRITE)
> +			mq->num_of_potential_packed_wr_reqs++;
>  		list_add_tail(&next->queuelist, &mq->mqrq_cur->packed_list);
>  		cur = next;
>  		reqs++;
> @@ -1780,7 +1860,9 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
>  		goto out;
>  	}
> 
> -	if (req && req->cmd_flags & REQ_DISCARD) {
> +	mmc_blk_write_packing_control(mq, req);
> +
> +	if (req && req->cmd_flags & REQ_DISCARD) {
>  		/* complete ongoing async transfer before issuing discard */
>  		if (card->host->areq)
>  			mmc_blk_issue_rw_rq(mq, NULL);
> @@ -2010,6 +2092,8 @@ static void mmc_blk_remove_req(struct mmc_blk_data *md)
> 
>  	if (md) {
>  		card = md->queue.card;
> +		device_remove_file(disk_to_dev(md->disk),
> +				   &md->num_wr_reqs_to_start_packing);
>  		if (md->disk->flags & GENHD_FL_UP) {
>  			device_remove_file(disk_to_dev(md->disk), &md->force_ro);
>  			if ((md->area_type & MMC_BLK_DATA_AREA_BOOT) &&
> @@ -2076,6 +2160,20 @@ static int mmc_add_disk(struct mmc_blk_data *md)
>  		if (ret)
>  			goto power_ro_lock_fail;
>  	}
> +
> +	md->num_wr_reqs_to_start_packing.show =
> +		num_wr_reqs_to_start_packing_show;
> +	md->num_wr_reqs_to_start_packing.store =
> +		num_wr_reqs_to_start_packing_store;
> +	sysfs_attr_init(&md->num_wr_reqs_to_start_packing.attr);
> +	md->num_wr_reqs_to_start_packing.attr.name =
> +		"num_wr_reqs_to_start_packing";
> +	md->num_wr_reqs_to_start_packing.attr.mode = S_IRUGO | S_IWUSR;
> +	ret = device_create_file(disk_to_dev(md->disk),
> +				 &md->num_wr_reqs_to_start_packing);
> +	if (ret)
> +		goto power_ro_lock_fail;
> +
>  	return ret;
> 
>  power_ro_lock_fail:
> diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
> index 165d85a..79ef91b 100644
> --- a/drivers/mmc/card/queue.c
> +++ b/drivers/mmc/card/queue.c
> @@ -25,6 +25,13 @@
>  #define MMC_QUEUE_SUSPENDED	(1 << 0)
> 
>  /*
> + * Based on benchmark tests the default num of requests to trigger the write
> + * packing was determined, to keep the read latency as low as possible and
> + * manage to keep the high write throughput.
> + */
> +#define DEFAULT_NUM_REQS_TO_START_PACK 17
> +
> +/*
>   * Prepare a MMC request. This just filters out odd stuff.
>   */
>  static int mmc_prep_request(struct request_queue *q, struct request *req)
> @@ -181,6 +188,7 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card,
>  	mq->mqrq_cur = mqrq_cur;
>  	mq->mqrq_prev = mqrq_prev;
>  	mq->queue->queuedata = mq;
> +	mq->num_wr_reqs_to_start_packing = DEFAULT_NUM_REQS_TO_START_PACK;
> 
>  	blk_queue_prep_rq(mq->queue, mmc_prep_request);
>  	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, mq->queue);
> diff --git a/drivers/mmc/card/queue.h b/drivers/mmc/card/queue.h
> index d761bf1..6c29e0e 100644
> --- a/drivers/mmc/card/queue.h
> +++ b/drivers/mmc/card/queue.h
> @@ -44,6 +44,9 @@ struct mmc_queue {
>  	struct mmc_queue_req	mqrq[2];
>  	struct mmc_queue_req	*mqrq_cur;
>  	struct mmc_queue_req	*mqrq_prev;
> +	bool			wr_packing_enabled;
> +	int			num_of_potential_packed_wr_reqs;
> +	int			num_wr_reqs_to_start_packing;
>  };
> 
>  extern int mmc_init_queue(struct mmc_queue *, struct mmc_card *, spinlock_t *,
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 9d0d946..0eb6c7b 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -242,6 +242,7 @@ struct mmc_host {
>  #define MMC_CAP2_PACKED_WR	(1 << 11)	/* Allow packed write */
>  #define MMC_CAP2_PACKED_CMD	(MMC_CAP2_PACKED_RD | \
>  				 MMC_CAP2_PACKED_WR) /* Allow packed commands */
> +#define MMC_CAP2_PACKED_WR_CONTROL (1 << 12) /* Allow write packing control */
> 
>  	mmc_pm_flag_t		pm_caps;	/* supported pm features */
>  	unsigned int        power_notify_type;
> --
> 1.7.3.3
> --
> Sent by a consultant of the Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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