[PATCH V8 03/20] mmc: queue: Fix queue thread wake-up

Adrian Hunter
2016-11-29T10:14:44Z

The only time the driver sleeps expecting to be woken upon the arrival of
a new request, is when the dispatch queue is empty. The only time that it
is known whether the dispatch queue is empty is after NULL is returned
from blk_fetch_request() while under the queue lock.

Recognizing those facts, simplify the synchronization between the queue
thread and the request function. A couple of flags tell the request
function what to do, and the queue lock and barriers associated with
wake-ups ensure synchronization.

The result is simpler and allows the removal of the context_info lock.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Harjani Ritesh <riteshh@codeaurora.org>
---
drivers/mmc/card/block.c | 7 -------
drivers/mmc/card/queue.c | 35 +++++++++++++++++++++--------------
drivers/mmc/card/queue.h | 1 +
drivers/mmc/core/core.c | 6 ------
include/linux/mmc/host.h | 2 --
5 files changed, 22 insertions(+), 29 deletions(-)

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 3e73be0e7281..646d1a1fa6ca 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -1758,8 +1758,6 @@ int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
int ret;
struct mmc_blk_data *md = mq->blkdata;
struct mmc_card *card = md->queue.card;
- struct mmc_host *host = card->host;
- unsigned long flags;
bool req_is_special = mmc_req_is_special(req);

if (req && !mq->mqrq_prev->req)
@@ -1792,11 +1790,6 @@ int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
mmc_blk_issue_rw_rq(mq, NULL);
ret = mmc_blk_issue_flush(mq, req);
} else {
- if (!req && host->areq) {
- spin_lock_irqsave(&host->context_info.lock, flags);
- host->context_info.is_waiting_last_req = true;
- spin_unlock_irqrestore(&host->context_info.lock, flags);
- }
ret = mmc_blk_issue_rw_rq(mq, req);
}

diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index 7dacf2744fbd..010888d8d97c 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -53,6 +53,7 @@ static int mmc_queue_thread(void *d)
{
struct mmc_queue *mq = d;
struct request_queue *q = mq->queue;
+ struct mmc_context_info *cntx = &mq->card->host->context_info;

current->flags |= PF_MEMALLOC;

@@ -63,6 +64,19 @@ static int mmc_queue_thread(void *d)
spin_lock_irq(q->queue_lock);
set_current_state(TASK_INTERRUPTIBLE);
req = blk_fetch_request(q);
+ mq->asleep = false;
+ cntx->is_waiting_last_req = false;
+ cntx->is_new_req = false;
+ if (!req) {
+ /*
+ * Dispatch queue is empty so set flags for
+ * mmc_request_fn() to wake us up.
+ */
+ if (mq->mqrq_prev->req)
+ cntx->is_waiting_last_req = true;
+ else
+ mq->asleep = true;
+ }
mq->mqrq_cur->req = req;
spin_unlock_irq(q->queue_lock);

@@ -115,7 +129,6 @@ 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) {
@@ -127,19 +140,13 @@ static void mmc_request_fn(struct request_queue *q)
}

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)
+
+ if (cntx->is_waiting_last_req) {
+ cntx->is_new_req = true;
+ wake_up_interruptible(&cntx->wait);
+ }
+
+ if (mq->asleep)
wake_up_process(mq->thread);
}

diff --git a/drivers/mmc/card/queue.h b/drivers/mmc/card/queue.h
index 47f5532b5776..d09fce655800 100644
--- a/drivers/mmc/card/queue.h
+++ b/drivers/mmc/card/queue.h
@@ -39,6 +39,7 @@ struct mmc_queue {
unsigned int flags;
#define MMC_QUEUE_SUSPENDED (1 << 0)
#define MMC_QUEUE_NEW_REQUEST (1 << 1)
+ bool asleep;
struct mmc_blk_data *blkdata;
struct request_queue *queue;
struct mmc_queue_req mqrq[2];
diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index f39397f7c8dc..dc1f27ee50b8 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -504,18 +504,14 @@ static enum mmc_blk_status mmc_wait_for_data_req_done(struct mmc_host *host,
struct mmc_command *cmd;
struct mmc_context_info *context_info = &host->context_info;
enum mmc_blk_status status;
- 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 ||
@@ -534,7 +530,6 @@ static enum mmc_blk_status mmc_wait_for_data_req_done(struct mmc_host *host,
continue; /* wait for done/new event again */
}
} else if (context_info->is_new_req) {
- context_info->is_new_req = false;
if (!next_req)
return MMC_BLK_NEW_REQUEST;
}
@@ -3016,7 +3011,6 @@ void mmc_unregister_pm_notifier(struct mmc_host *host)
*/
void mmc_init_context_info(struct mmc_host *host)
{
- 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;
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 2ce32fefb41c..8bc884121465 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -197,14 +197,12 @@ struct mmc_slot {
* @is_new_req wake up reason was new request
* @is_waiting_last_req mmc context waiting for single running request
* @wait wait queue
- * @lock lock to protect data fields
*/
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 regulator;
--
1.9.1