Hi,
How can we check the effect?
Do you have any result?
Please check the several comment below.
Maya Erez <merez@xxxxxxxxxxxxxx> 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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