Message-ID: <bdda84067f732d4b7bba9dec06f2a02c.squirrel@www.codeaurora.org>
Date:	Mon, 8 Oct 2012 20:52:08 -0700 (PDT)
From:	merez@...eaurora.org
To:	"Maya Erez" <merez@...eaurora.org>
Cc:	linux-mmc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	"Maya Erez" <merez@...eaurora.org>,
	"Jaehoon Chung" <jh80.chung@...sung.com>,
	"open list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mmc: core: Add support for idle time BKOPS

Hi Chris and all,

According to the eMMC4.5 standard, a host that enables the BKOPS_EN bit
must also check the BKOPS status periodically:
"Host shall check the status periodically and start background operations
as needed, so that the device has enough time for its maintenance
operations, to help reduce the latencies during foreground operations. If
the status is at level 3 ("critical"), some operations may extend beyond
their original timeouts due to maintenance operations which cannot be
delayed anymore. The host should give the device enough time for
background operations to avoid getting to this level in the first place."

As mentioned in the standard quotation above, it is not recommended to
handle only BKOPS of level 3 since it can lead to foreground operations
timeout.

I would appreciate if you could review this change to add the periodic
BKOPS on top of handling BKOPS level 3 that was already mainlined.

Thnaks,
Maya
On Thu, October 4, 2012 3:28 pm, Maya Erez wrote:
> Devices have various maintenance operations need to perform internally.
> In order to reduce latencies during time critical operations like read
> and write, it is better to execute maintenance operations in other
> times - when the host is not being serviced. Such operations are called
> Background operations (BKOPS).
> The device notifies the status of the BKOPS need by updating BKOPS_STATUS
> (EXT_CSD byte [246]).
>
> According to the standard a host that supports BKOPS shall check the
> status periodically and start background operations as needed, so that
> the device has enough time for its maintenance operations.
>
> This patch adds support for this periodic check of the BKOPS status.
> Since foreground operations are of higher priority than background
> operations the host will check the need for BKOPS when it is idle,
> and in case of an incoming request the BKOPS operation will be
> interrupted.
>
> When the mmcqd thread is idle, a delayed work is created to check the
> need for BKOPS. The time to start the delayed work is calculated based
> on the host controller suspend timeout, in case it was set. If not, a
> default time is used.
> If BKOPS are required in level 1, which is non-blocking, there will be
> polling of the card status to wait for the BKOPS completion and prevent
> suspend that will interrupt the BKOPS.
> If the card raised an exception, the need for urgent BKOPS (level 2/3)
> will be checked immediately and if needed, the BKOPS will be performed
> without waiting for the next idle time.
>
> Signed-off-by: Maya Erez <merez@...eaurora.org>
> Signed-off-by: Jaehoon Chung <jh80.chung@...sung.com>
> ---
> This patch is based on the periodic BKOPS implementation in version 8 of
> "support BKOPS feature for eMMC" patch.
> The patch was modified to answer the following issues:
> - In order to prevent a race condition between going into suspend and
> starting BKOPS,
>   the suspend timeout of the host controller is taking into accound in
> determination of the start time
>   of the delayed work
> - Since mmc_start_bkops is called from two contexts now, mmc_claim_host
> was moved to the beginning of the function
> - Also, the check of doing_bkops should be protected when determing if an
> HPI is needed due to the same reason.
> - Starting and canceling the delayed work in each idle caused degradation
> of iozone performance. Therefore,
>   the delayed work is not started on each idle. The amount of sectors
> changed (written or discard) from the last
>   delayed work is the trigger for starting the delayed BKOPS work.
> ---
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index 172a768..ed040d5 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -827,6 +827,9 @@ static int mmc_blk_issue_discard_rq(struct mmc_queue
> *mq, struct request *req)
>  	from = blk_rq_pos(req);
>  	nr = blk_rq_sectors(req);
>
> +	if (card->ext_csd.bkops_en)
> +		card->bkops_info.sectors_changed += blk_rq_sectors(req);
> +
>  	if (mmc_can_discard(card))
>  		arg = MMC_DISCARD_ARG;
>  	else if (mmc_can_trim(card))
> @@ -1268,6 +1271,9 @@ static int mmc_blk_issue_rw_rq(struct mmc_queue *mq,
> struct request *rqc)
>  	if (!rqc && !mq->mqrq_prev->req)
>  		return 0;
>
> +	if (rqc && (card->ext_csd.bkops_en) && (rq_data_dir(rqc) == WRITE))
> +			card->bkops_info.sectors_changed += blk_rq_sectors(rqc);
> +
>  	do {
>  		if (rqc) {
>  			/*
> diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
> index e360a97..e96f5cf 100644
> --- a/drivers/mmc/card/queue.c
> +++ b/drivers/mmc/card/queue.c
> @@ -51,6 +51,7 @@ static int mmc_queue_thread(void *d)
>  {
>  	struct mmc_queue *mq = d;
>  	struct request_queue *q = mq->queue;
> +	struct mmc_card *card = mq->card;
>
>  	current->flags |= PF_MEMALLOC;
>
> @@ -66,6 +67,17 @@ static int mmc_queue_thread(void *d)
>  		spin_unlock_irq(q->queue_lock);
>
>  		if (req || mq->mqrq_prev->req) {
> +			/*
> +			 * If this is the first request, BKOPs might be in
> +			 * progress and needs to be stopped before issuing the
> +			 * request
> +			 */
> +			if (card->ext_csd.bkops_en &&
> +			    card->bkops_info.started_delayed_bkops) {
> +				card->bkops_info.started_delayed_bkops = false;
> +				mmc_stop_bkops(card);
> +			}
> +
>  			set_current_state(TASK_RUNNING);
>  			mq->issue_fn(mq, req);
>  		} else {
> @@ -73,6 +85,7 @@ static int mmc_queue_thread(void *d)
>  				set_current_state(TASK_RUNNING);
>  				break;
>  			}
> +			mmc_start_delayed_bkops(card);
>  			up(&mq->thread_sem);
>  			schedule();
>  			down(&mq->thread_sem);
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 6612163..fd8783d 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -253,9 +253,42 @@ mmc_start_request(struct mmc_host *host, struct
> mmc_request *mrq)
>  }
>
>  /**
> + * mmc_start_delayed_bkops() - Start a delayed work to check for
> + *      the need of non urgent BKOPS
> + *
> + * @card: MMC card to start BKOPS on
> + */
> +void mmc_start_delayed_bkops(struct mmc_card *card)
> +{
> +	if (!card || !card->ext_csd.bkops_en || mmc_card_doing_bkops(card))
> +		return;
> +
> +	if (card->bkops_info.sectors_changed <
> +	    BKOPS_MIN_SECTORS_TO_QUEUE_DELAYED_WORK)
> +		return;
> +
> +	pr_debug("%s: %s: queueing delayed_bkops_work\n",
> +		 mmc_hostname(card->host), __func__);
> +
> +	card->bkops_info.sectors_changed = 0;
> +
> +	/*
> +	 * cancel_delayed_bkops_work will prevent a race condition between
> +	 * fetching a request by the mmcqd and the delayed work, in case
> +	 * it was removed from the queue work but not started yet
> +	 */
> +	card->bkops_info.cancel_delayed_work = false;
> +	card->bkops_info.started_delayed_bkops = true;
> +	queue_delayed_work(system_nrt_wq, &card->bkops_info.dw,
> +			   msecs_to_jiffies(
> +				   card->bkops_info.delay_ms));
> +}
> +EXPORT_SYMBOL(mmc_start_delayed_bkops);
> +
> +/**
>   *	mmc_start_bkops - start BKOPS for supported cards
>   *	@card: MMC card to start BKOPS
> - *	@form_exception: A flag to indicate if this function was
> + *	@from_exception: A flag to indicate if this function was
>   *			 called due to an exception raised by the card
>   *
>   *	Start background operations whenever requested.
> @@ -269,25 +302,47 @@ void mmc_start_bkops(struct mmc_card *card, bool
> from_exception)
>  	bool use_busy_signal;
>
>  	BUG_ON(!card);
> -
> -	if (!card->ext_csd.bkops_en || mmc_card_doing_bkops(card))
> +	if (!card->ext_csd.bkops_en)
>  		return;
>
> +	mmc_claim_host(card->host);
> +
> +	if ((card->bkops_info.cancel_delayed_work) && !from_exception) {
> +		pr_debug("%s: %s: cancel_delayed_work was set, exit\n",
> +			 mmc_hostname(card->host), __func__);
> +		card->bkops_info.cancel_delayed_work = false;
> +		goto out;
> +	}
> +
> +	if (mmc_card_doing_bkops(card)) {
> +		pr_debug("%s: %s: already doing bkops, exit\n",
> +			 mmc_hostname(card->host), __func__);
> +		goto out;
> +	}
> +
>  	err = mmc_read_bkops_status(card);
>  	if (err) {
>  		pr_err("%s: Failed to read bkops status: %d\n",
>  		       mmc_hostname(card->host), err);
> -		return;
> +		goto out;
>  	}
>
>  	if (!card->ext_csd.raw_bkops_status)
> -		return;
> +		goto out;
> +
> +	pr_info("%s: %s: card->ext_csd.raw_bkops_status = 0x%x\n",
> +		mmc_hostname(card->host), __func__,
> +		card->ext_csd.raw_bkops_status);
>
> +	/*
> +	 * If the function was called due to exception but there is no need
> +	 * for urgent BKOPS, BKOPs will be performed by the delayed BKOPs
> +	 * work, before going to suspend
> +	 */
>  	if (card->ext_csd.raw_bkops_status < EXT_CSD_BKOPS_LEVEL_2 &&
>  	    from_exception)
> -		return;
> +		goto out;
>
> -	mmc_claim_host(card->host);
>  	if (card->ext_csd.raw_bkops_status >= EXT_CSD_BKOPS_LEVEL_2) {
>  		timeout = MMC_BKOPS_MAX_TIMEOUT;
>  		use_busy_signal = true;
> @@ -309,13 +364,108 @@ void mmc_start_bkops(struct mmc_card *card, bool
> from_exception)
>  	 * bkops executed synchronously, otherwise
>  	 * the operation is in progress
>  	 */
> -	if (!use_busy_signal)
> +	if (!use_busy_signal) {
>  		mmc_card_set_doing_bkops(card);
> +		pr_debug("%s: %s: starting the polling thread\n",
> +			 mmc_hostname(card->host), __func__);
> +		queue_work(system_nrt_wq,
> +			   &card->bkops_info.poll_for_completion);
> +	}
> +
>  out:
>  	mmc_release_host(card->host);
>  }
>  EXPORT_SYMBOL(mmc_start_bkops);
>
> +/**
> + * mmc_bkops_completion_polling() - Poll on the card status to
> + * wait for the non-blocking BKOPS completion
> + * @work:	The completion polling work
> + *
> + * The on-going reading of the card status will prevent the card
> + * from getting into suspend while it is in the middle of
> + * performing BKOPS.
> + * Since the non blocking BKOPS can be interrupted by a fetched
> + * request we also check IF mmc_card_doing_bkops in each
> + * iteration.
> + */
> +void mmc_bkops_completion_polling(struct work_struct *work)
> +{
> +	struct mmc_card *card = container_of(work, struct mmc_card,
> +			bkops_info.poll_for_completion);
> +	unsigned long timeout_jiffies = jiffies +
> +		msecs_to_jiffies(BKOPS_COMPLETION_POLLING_TIMEOUT_MS);
> +	u32 status;
> +	int err;
> +
> +	/*
> +	 * Wait for the BKOPs to complete. Keep reading the status to prevent
> +	 * the host from getting into suspend
> +	 */
> +	do {
> +		mmc_claim_host(card->host);
> +
> +		if (!mmc_card_doing_bkops(card))
> +			goto out;
> +
> +		err = mmc_send_status(card, &status);
> +		if (err) {
> +			pr_err("%s: error %d requesting status\n",
> +			       mmc_hostname(card->host), err);
> +			goto out;
> +		}
> +
> +		/*
> +		 * Some cards mishandle the status bits, so make sure to check
> +		 * both the busy indication and the card state.
> +		 */
> +		if ((status & R1_READY_FOR_DATA) &&
> +		    (R1_CURRENT_STATE(status) != R1_STATE_PRG)) {
> +			pr_debug("%s: %s: completed BKOPs, exit polling\n",
> +				 mmc_hostname(card->host), __func__);
> +			mmc_card_clr_doing_bkops(card);
> +			card->bkops_info.started_delayed_bkops = false;
> +			goto out;
> +		}
> +
> +		mmc_release_host(card->host);
> +
> +		/*
> +		 * Sleep before checking the card status again to allow the
> +		 * card to complete the BKOPs operation
> +		 */
> +		msleep(BKOPS_COMPLETION_POLLING_INTERVAL_MS);
> +	} while (time_before(jiffies, timeout_jiffies));
> +
> +	pr_err("%s: %s: exit polling due to timeout\n",
> +	       mmc_hostname(card->host), __func__);
> +
> +	return;
> +out:
> +	mmc_release_host(card->host);
> +}
> +
> +/**
> + * mmc_start_idle_time_bkops() - check if a non urgent BKOPS is
> + * needed
> + * @work:	The idle time BKOPS work
> + */
> +void mmc_start_idle_time_bkops(struct work_struct *work)
> +{
> +	struct mmc_card *card = container_of(work, struct mmc_card,
> +			bkops_info.dw.work);
> +
> +	/*
> +	 * Prevent a race condition between mmc_stop_bkops and the delayed
> +	 * BKOPS work in case the delayed work is executed on another CPU
> +	 */
> +	if (card->bkops_info.cancel_delayed_work)
> +		return;
> +
> +	mmc_start_bkops(card, false);
> +}
> +EXPORT_SYMBOL(mmc_start_idle_time_bkops);
> +
>  static void mmc_wait_done(struct mmc_request *mrq)
>  {
>  	complete(&mrq->completion);
> @@ -582,6 +732,19 @@ int mmc_stop_bkops(struct mmc_card *card)
>  	int err = 0;
>
>  	BUG_ON(!card);
> +
> +	mmc_claim_host(card->host);
> +
> +	/*
> +	 * Notify the delayed work to be cancelled, in case it was already
> +	 * removed from the queue, but was not started yet
> +	 */
> +	card->bkops_info.cancel_delayed_work = true;
> +	if (delayed_work_pending(&card->bkops_info.dw))
> +		cancel_delayed_work_sync(&card->bkops_info.dw);
> +	if (!mmc_card_doing_bkops(card))
> +		goto out;
> +
>  	err = mmc_interrupt_hpi(card);
>
>  	/*
> @@ -593,6 +756,8 @@ int mmc_stop_bkops(struct mmc_card *card)
>  		err = 0;
>  	}
>
> +out:
> +	mmc_release_host(card->host);
>  	return err;
>  }
>  EXPORT_SYMBOL(mmc_stop_bkops);
> @@ -2566,15 +2731,13 @@ int mmc_pm_notify(struct notifier_block
> *notify_block,
>  	switch (mode) {
>  	case PM_HIBERNATION_PREPARE:
>  	case PM_SUSPEND_PREPARE:
> -		if (host->card && mmc_card_mmc(host->card) &&
> -		    mmc_card_doing_bkops(host->card)) {
> +		if (host->card && mmc_card_mmc(host->card)) {
>  			err = mmc_stop_bkops(host->card);
>  			if (err) {
>  				pr_err("%s: didn't stop bkops\n",
>  					mmc_hostname(host));
>  				return err;
>  			}
> -			mmc_card_clr_doing_bkops(host->card);
>  		}
>
>  		spin_lock_irqsave(&host->lock, flags);
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 7509de1..f8ff640 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1258,6 +1258,30 @@ static int mmc_init_card(struct mmc_host *host, u32
> ocr,
>  		}
>  	}
>
> +	if (!oldcard) {
> +		if (card->ext_csd.bkops_en) {
> +			INIT_DELAYED_WORK(&card->bkops_info.dw,
> +					  mmc_start_idle_time_bkops);
> +			INIT_WORK(&card->bkops_info.poll_for_completion,
> +				  mmc_bkops_completion_polling);
> +
> +			/*
> +			 * Calculate the time to start the BKOPs checking.
> +			 * The idle time of the host controller should be taken
> +			 * into account in order to prevent a race condition
> +			 * before starting BKOPs and going into suspend.
> +			 * If the host controller didn't set its idle time,
> +			 * a default value is used.
> +			 */
> +			card->bkops_info.delay_ms = MMC_IDLE_BKOPS_TIME_MS;
> +			if (card->bkops_info.host_suspend_tout_ms)
> +				card->bkops_info.delay_ms = min(
> +					card->bkops_info.delay_ms,
> +				      card->bkops_info.host_suspend_tout_ms/2);
> +
> +		}
> +	}
> +
>  	if (!oldcard)
>  		host->card = card;
>
> diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
> index 78cc3be..0e4d55a 100644
> --- a/include/linux/mmc/card.h
> +++ b/include/linux/mmc/card.h
> @@ -207,6 +207,48 @@ struct mmc_part {
>  #define MMC_BLK_DATA_AREA_GP	(1<<2)
>  };
>
> +/**
> + * struct mmc_bkops_info - BKOPS data
> + * @dw:	Idle time bkops delayed work
> + * @host_suspend_tout_ms:	The host controller idle time,
> + * before getting into suspend
> + * @delay_ms:	The time to start the BKOPS
> + *        delayed work once MMC thread is idle
> + * @poll_for_completion:	Poll on BKOPS completion
> + * @cancel_delayed_work: A flag to indicate if the delayed work
> + *        should be cancelled
> + * @started_delayed_bkops:  A flag to indicate if the delayed
> + *        work was scheduled
> + * @sectors_changed:  number of  sectors written or
> + *       discard since the last idle BKOPS were scheduled
> + */
> +struct mmc_bkops_info {
> +	struct delayed_work	dw;
> +	unsigned int		host_suspend_tout_ms;
> +	unsigned int		delay_ms;
> +/*
> + * A default time for checking the need for non urgent BKOPS once mmcqd
> + * is idle.
> + */
> +#define MMC_IDLE_BKOPS_TIME_MS 2000
> +	struct work_struct	poll_for_completion;
> +/* Polling timeout and interval for waiting on non-blocking BKOPs
> completion */
> +#define BKOPS_COMPLETION_POLLING_TIMEOUT_MS 10000 /* in ms */
> +#define BKOPS_COMPLETION_POLLING_INTERVAL_MS 1000 /* in ms */
> +	bool			cancel_delayed_work;
> +	bool			started_delayed_bkops;
> +	unsigned int		sectors_changed;
> +/*
> + * Since canceling the delayed work might have significant effect on the
> + * performance of small requests we won't queue the delayed work every
> time
> + * mmcqd thread is idle.
> + * The delayed work for idle BKOPS will be scheduled only after a
> significant
> + * amount of write or discard data.
> + * 100MB is chosen based on benchmark tests.
> + */
> +#define BKOPS_MIN_SECTORS_TO_QUEUE_DELAYED_WORK 204800 /* 100MB */
> +};
> +
>  /*
>   * MMC device
>   */
> @@ -281,6 +323,8 @@ struct mmc_card {
>  	struct dentry		*debugfs_root;
>  	struct mmc_part	part[MMC_NUM_PHY_PARTITION]; /* physical partitions */
>  	unsigned int    nr_parts;
> +
> +	struct mmc_bkops_info	bkops_info;
>  };
>
>  /*
> diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
> index 9b9cdaf..665d345 100644
> --- a/include/linux/mmc/core.h
> +++ b/include/linux/mmc/core.h
> @@ -145,6 +145,9 @@ extern int mmc_app_cmd(struct mmc_host *, struct
> mmc_card *);
>  extern int mmc_wait_for_app_cmd(struct mmc_host *, struct mmc_card *,
>  	struct mmc_command *, int);
>  extern void mmc_start_bkops(struct mmc_card *card, bool from_exception);
> +extern void mmc_start_delayed_bkops(struct mmc_card *card);
> +extern void mmc_start_idle_time_bkops(struct work_struct *work);
> +extern void mmc_bkops_completion_polling(struct work_struct *work);
>  extern int __mmc_switch(struct mmc_card *, u8, u8, u8, unsigned int,
> bool);
>  extern int mmc_switch(struct mmc_card *, u8, u8, u8, unsigned int);
>
> --
> 1.7.6
> --
> QUALCOMM ISRAEL, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation
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