RE: [PATCH v4] mmc: fix async request mechanism for sequential read scenarios

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

Hi,

Doesn't it consider SD path?
It have a problem with uninitialized 'context_info'.
'context_info' is moved into mmc_host struct in v4.
Please, could you explain the reason in brief?

Thanks,
Seungwon Jeon

On Wednesday, December 05, 2012, Konstantin Dorfman wrote:
> When current request is running on the bus and if next request fetched
> by mmcqd is NULL, mmc context (mmcqd thread) gets blocked until the
> current request completes. This means if new request comes in while
> the mmcqd thread is blocked, this new request can not be prepared in
> parallel to current ongoing request. This may result in latency to
> start new request.
> 
> This change allows to wake up the MMC thread (which
> is waiting for the current running request to complete). Now once the
> MMC thread is woken up, new request can be fetched and prepared in
> parallel to current running request which means this new request can
> be started immediately after the current running request completes.
> 
> With this change read throughput is improved by 16%.
> 
> Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>
> ---
> v4:     keeps new synchronization mechanism within mmc/core
> 	layer, so mmc/core external API's are not changed.
> 	- context_info moved into mmc_host struct
> 	- context_info initialized in mmc_attach_mmc()
> 
> v3:
> 	- new MMC_QUEUE_NEW_REQUEST flag to mark new request case
> 	- lock added to update is_new_req flag
> 	- condition for sending new req notification changed
> 	- Moved start waiting for new req notification
> 	  after fetching NULL
> v2:
> 	- Removed synchronization flags
> 	- removed lock from done()
> 	- flags names changed
> v1:
> 	- Initial submit
> 
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index 21056b9..f4f295e 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -113,17 +113,6 @@ struct mmc_blk_data {
> 
>  static DEFINE_MUTEX(open_lock);
> 
> -enum mmc_blk_status {
> -	MMC_BLK_SUCCESS = 0,
> -	MMC_BLK_PARTIAL,
> -	MMC_BLK_CMD_ERR,
> -	MMC_BLK_RETRY,
> -	MMC_BLK_ABORT,
> -	MMC_BLK_DATA_ERR,
> -	MMC_BLK_ECC_ERR,
> -	MMC_BLK_NOMEDIUM,
> -};
> -
>  module_param(perdev_minors, int, 0444);
>  MODULE_PARM_DESC(perdev_minors, "Minors numbers to allocate per device");
> 
> @@ -1363,9 +1352,12 @@ static int mmc_blk_issue_rw_rq(struct mmc_queue *mq, struct request *rqc)
>  			areq = &mq->mqrq_cur->mmc_active;
>  		} else
>  			areq = NULL;
> -		areq = mmc_start_req(card->host, areq, (int *) &status);
> -		if (!areq)
> +		areq = mmc_start_req(card->host, areq, (int *)&status);
> +		if (!areq) {
> +			if (status == MMC_BLK_NEW_REQUEST)
> +				mq->flags |= MMC_QUEUE_NEW_REQUEST;
>  			return 0;
> +		}
> 
>  		mq_rq = container_of(areq, struct mmc_queue_req, mmc_active);
>  		brq = &mq_rq->brq;
> @@ -1374,6 +1366,8 @@ static int mmc_blk_issue_rw_rq(struct mmc_queue *mq, struct request *rqc)
>  		mmc_queue_bounce_post(mq_rq);
> 
>  		switch (status) {
> +		case MMC_BLK_NEW_REQUEST:
> +			BUG(); /* should never get here */
>  		case MMC_BLK_SUCCESS:
>  		case MMC_BLK_PARTIAL:
>  			/*
> @@ -1486,6 +1480,7 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
>  		goto out;
>  	}
> 
> +	mq->flags &= ~MMC_QUEUE_NEW_REQUEST;
>  	if (req && req->cmd_flags & REQ_DISCARD) {
>  		/* complete ongoing async transfer before issuing discard */
>  		if (card->host->areq)
> @@ -1505,7 +1500,7 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
>  	}
> 
>  out:
> -	if (!req)
> +	if (!req && !(mq->flags & MMC_QUEUE_NEW_REQUEST))
>  		/* release host only when there are no more requests */
>  		mmc_release_host(card->host);
>  	return ret;
> diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
> index fadf52e..0c37b49 100644
> --- a/drivers/mmc/card/queue.c
> +++ b/drivers/mmc/card/queue.c
> @@ -22,7 +22,6 @@
> 
>  #define MMC_QUEUE_BOUNCESZ	65536
> 
> -#define MMC_QUEUE_SUSPENDED	(1 << 0)
> 
>  /*
>   * Prepare a MMC request. This just filters out odd stuff.
> @@ -63,11 +62,20 @@ static int mmc_queue_thread(void *d)
>  		set_current_state(TASK_INTERRUPTIBLE);
>  		req = blk_fetch_request(q);
>  		mq->mqrq_cur->req = req;
> +		if (!req && mq->mqrq_prev->req &&
> +			!(mq->mqrq_prev->req->cmd_flags & REQ_FLUSH) &&
> +			!(mq->mqrq_prev->req->cmd_flags & REQ_DISCARD))
> +			mq->card->host->context_info.is_waiting_last_req = true;
> +
>  		spin_unlock_irq(q->queue_lock);
> 
>  		if (req || mq->mqrq_prev->req) {
>  			set_current_state(TASK_RUNNING);
>  			mq->issue_fn(mq, req);
> +			if (mq->flags & MMC_QUEUE_NEW_REQUEST) {
> +				mq->flags &= ~MMC_QUEUE_NEW_REQUEST;
> +				continue; /* fetch again */
> +			}
> 
>  			/*
>  			 * Current request becomes previous request
> @@ -103,6 +111,8 @@ static void mmc_request_fn(struct request_queue *q)
>  {
>  	struct mmc_queue *mq = q->queuedata;
>  	struct request *req;
> +	unsigned long flags;
> +	struct mmc_context_info *cntx;
> 
>  	if (!mq) {
>  		while ((req = blk_fetch_request(q)) != NULL) {
> @@ -112,7 +122,20 @@ static void mmc_request_fn(struct request_queue *q)
>  		return;
>  	}
> 
> -	if (!mq->mqrq_cur->req && !mq->mqrq_prev->req)
> +	cntx = &mq->card->host->context_info;
> +	if (!mq->mqrq_cur->req && mq->mqrq_prev->req) {
> +		/*
> +		 * New MMC request arrived when MMC thread may be
> +		 * blocked on the previous request to be complete
> +		 * with no current request fetched
> +		 */
> +		spin_lock_irqsave(&cntx->lock, flags);
> +		if (cntx->is_waiting_last_req) {
> +			cntx->is_new_req = true;
> +			wake_up_interruptible(&cntx->wait);
> +		}
> +		spin_unlock_irqrestore(&cntx->lock, flags);
> +	} else if (!mq->mqrq_cur->req && !mq->mqrq_prev->req)
>  		wake_up_process(mq->thread);
>  }
> 
> diff --git a/drivers/mmc/card/queue.h b/drivers/mmc/card/queue.h
> index d2a1eb4..970d9e7 100644
> --- a/drivers/mmc/card/queue.h
> +++ b/drivers/mmc/card/queue.h
> @@ -26,6 +26,8 @@ struct mmc_queue {
>  	struct mmc_card		*card;
>  	struct task_struct	*thread;
>  	struct semaphore	thread_sem;
> +#define MMC_QUEUE_SUSPENDED	(1 << 0)
> +#define MMC_QUEUE_NEW_REQUEST	(1 << 1)
>  	unsigned int		flags;
>  	int			(*issue_fn)(struct mmc_queue *, struct request *);
>  	void			*data;
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index aaed768..855336d 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -319,11 +319,44 @@ out:
>  }
>  EXPORT_SYMBOL(mmc_start_bkops);
> 
> +/*
> + * mmc_wait_data_done() - done callback for data request
> + * @mrq: done data request
> + *
> + * Wakes up mmc context, passed as callback to host controller driver
> + */
> +static void mmc_wait_data_done(struct mmc_request *mrq)
> +{
> +	mrq->host->context_info.is_done_rcv = true;
> +	wake_up_interruptible(&mrq->host->context_info.wait);
> +}
> +
>  static void mmc_wait_done(struct mmc_request *mrq)
>  {
>  	complete(&mrq->completion);
>  }
> 
> +/*
> + *__mmc_start_data_req() - starts data request
> + * @host: MMC host to start the request
> + * @mrq: data request to start
> + *
> + * Fills done callback that will be used when request are done by card.
> + * Starts data mmc request execution
> + */
> +static int __mmc_start_data_req(struct mmc_host *host, struct mmc_request *mrq)
> +{
> +	mrq->done = mmc_wait_data_done;
> +	mrq->host = host;
> +	if (mmc_card_removed(host->card)) {
> +		mrq->cmd->error = -ENOMEDIUM;
> +		return -ENOMEDIUM;
> +	}
> +	mmc_start_request(host, mrq);
> +
> +	return 0;
> +}
> +
>  static int __mmc_start_req(struct mmc_host *host, struct mmc_request *mrq)
>  {
>  	init_completion(&mrq->completion);
> @@ -337,6 +370,60 @@ static int __mmc_start_req(struct mmc_host *host, struct mmc_request *mrq)
>  	return 0;
>  }
> 
> +/*
> + * mmc_wait_for_data_req_done() - wait for request completed or new
> + *				  request notification arrives
> + * @host: MMC host to prepare the command.
> + * @mrq: MMC request to wait for
> + *
> + * Blocks MMC context till host controller will ack end of data request
> + * execution or new request arrives from block layer. Handles
> + * command retries.
> + *
> + * Returns enum mmc_blk_status after checking errors.
> + */
> +static int mmc_wait_for_data_req_done(struct mmc_host *host,
> +				      struct mmc_request *mrq)
> +{
> +	struct mmc_command *cmd;
> +	struct mmc_context_info *context_info = &host->context_info;
> +	int err;
> +	unsigned long flags;
> +
> +	while (1) {
> +		wait_event_interruptible(context_info->wait,
> +				(context_info->is_done_rcv ||
> +				 context_info->is_new_req));
> +		spin_lock_irqsave(&context_info->lock, flags);
> +		context_info->is_waiting_last_req = false;
> +		spin_unlock_irqrestore(&context_info->lock, flags);
> +		if (context_info->is_done_rcv) {
> +			context_info->is_done_rcv = false;
> +			context_info->is_new_req = false;
> +			cmd = mrq->cmd;
> +			if (!cmd->error || !cmd->retries ||
> +					mmc_card_removed(host->card)) {
> +				err = host->areq->err_check(host->card,
> +						host->areq);
> +				break; /* return err */
> +			} else {
> +				pr_info("%s: req failed (CMD%u): %d, retrying...\n",
> +						mmc_hostname(host),
> +						cmd->opcode, cmd->error);
> +				cmd->retries--;
> +				cmd->error = 0;
> +				host->ops->request(host, mrq);
> +				continue; /* wait for done/new event again */
> +			}
> +		} else if (context_info->is_new_req) {
> +			context_info->is_new_req = false;
> +			err = MMC_BLK_NEW_REQUEST;
> +			break; /* return err */
> +		}
> +	} /* while */
> +	return err;
> +}
> +
>  static void mmc_wait_for_req_done(struct mmc_host *host,
>  				  struct mmc_request *mrq)
>  {
> @@ -426,8 +513,21 @@ struct mmc_async_req *mmc_start_req(struct mmc_host *host,
>  		mmc_pre_req(host, areq->mrq, !host->areq);
> 
>  	if (host->areq) {
> -		mmc_wait_for_req_done(host, host->areq->mrq);
> -		err = host->areq->err_check(host->card, host->areq);
> +		err = mmc_wait_for_data_req_done(host, host->areq->mrq);
> +		if (err == MMC_BLK_NEW_REQUEST) {
> +			if (areq) {
> +				pr_err("%s: new request while areq = %p",
> +						mmc_hostname(host), areq);
> +				BUG_ON(1);
> +			}
> +			if (error)
> +				*error = err;
> +			/*
> +			 * The previous request was not completed,
> +			 * nothing to return
> +			 */
> +			return NULL;
> +		}
>  		/*
>  		 * Check BKOPS urgency for each R1 response
>  		 */
> @@ -439,7 +539,7 @@ struct mmc_async_req *mmc_start_req(struct mmc_host *host,
>  	}
> 
>  	if (!err && areq)
> -		start_err = __mmc_start_req(host, areq->mrq);
> +		start_err = __mmc_start_data_req(host, areq->mrq);
> 
>  	if (host->areq)
>  		mmc_post_req(host, host->areq->mrq, 0);
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index e6e3911..dd3bc11 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -1497,6 +1497,12 @@ int mmc_attach_mmc(struct mmc_host *host)
>  	BUG_ON(!host);
>  	WARN_ON(!host->claimed);
> 
> +	spin_lock_init(&host->context_info.lock);
> +	host->context_info.is_new_req = false;
> +	host->context_info.is_done_rcv = false;
> +	host->context_info.is_waiting_last_req = false;
> +	init_waitqueue_head(&host->context_info.wait);
> +
>  	/* Set correct bus mode for MMC before attempting attach */
>  	if (!mmc_host_is_spi(host))
>  		mmc_set_bus_mode(host, MMC_BUSMODE_OPENDRAIN);
> diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
> index 5c69315..be2500a 100644
> --- a/include/linux/mmc/card.h
> +++ b/include/linux/mmc/card.h
> @@ -187,6 +187,18 @@ struct sdio_func_tuple;
> 
>  #define SDIO_MAX_FUNCS		7
> 
> +enum mmc_blk_status {
> +	MMC_BLK_SUCCESS = 0,
> +	MMC_BLK_PARTIAL,
> +	MMC_BLK_CMD_ERR,
> +	MMC_BLK_RETRY,
> +	MMC_BLK_ABORT,
> +	MMC_BLK_DATA_ERR,
> +	MMC_BLK_ECC_ERR,
> +	MMC_BLK_NOMEDIUM,
> +	MMC_BLK_NEW_REQUEST,
> +};
> +
>  /* The number of MMC physical partitions.  These consist of:
>   * boot partitions (2), general purpose partitions (4) in MMC v4.4.
>   */
> diff --git a/include/linux/mmc/core.h b/include/linux/mmc/core.h
> index 5bf7c22..724cc95 100644
> --- a/include/linux/mmc/core.h
> +++ b/include/linux/mmc/core.h
> @@ -120,6 +120,7 @@ struct mmc_data {
>  	s32			host_cookie;	/* host private data */
>  };
> 
> +struct mmc_host;
>  struct mmc_request {
>  	struct mmc_command	*sbc;		/* SET_BLOCK_COUNT for multiblock */
>  	struct mmc_command	*cmd;
> @@ -128,9 +129,9 @@ struct mmc_request {
> 
>  	struct completion	completion;
>  	void			(*done)(struct mmc_request *);/* completion function */
> +	struct mmc_host         *host;
>  };
> 
> -struct mmc_host;
>  struct mmc_card;
>  struct mmc_async_req;
> 
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index 23df21e..08a8203 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -176,6 +176,21 @@ struct mmc_supply {
>  	struct regulator *vqmmc;	/* Optional Vccq supply */
>  };
> 
> +/**
> + * mmc_context_info - synchronization details for mmc context
> + * @is_done_rcv		wake up reason was done request
> + * @is_new_req	wake up reason was new request
> + * @is_waiting_last_req	mmc context waiting for single running request
> + * @wait		wait queue
> + */
> +struct mmc_context_info {
> +	bool			is_done_rcv;
> +	bool			is_new_req;
> +	bool			is_waiting_last_req;
> +	wait_queue_head_t	wait;
> +	spinlock_t		lock;
> +};
> +
>  struct mmc_host {
>  	struct device		*parent;
>  	struct device		class_dev;
> @@ -330,6 +345,7 @@ struct mmc_host {
>  	struct dentry		*debugfs_root;
> 
>  	struct mmc_async_req	*areq;		/* active async req */
> +	struct mmc_context_info context_info;   /* async synchronization info */
> 
>  #ifdef CONFIG_FAIL_MMC_REQUEST
>  	struct fault_attr	fail_mmc_request;
> --
> 1.7.6
> --
> Konstantin Dorfman,
> 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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