[PATCH V5 08/13] blk-mq: return budget token from .get_budget callback

Ming Lei
2020-11-19T09:35:25Z

SCSI uses one global atomic variable to track queue depth for each
LUN/request queue.

This way doesn't scale well when there is lots of CPU cores and the
disk is very fast. It has been observed that IOPS is affected a lot
by tracking queue depth via sdev->device_busy in IO path.

Return budget token from .get_budget callback, and the budget token
can be passed to driver, so that we can replace the atomic variable
with sbitmap_queue, then the scale issue can be fixed.

Cc: Omar Sandoval <osandov@fb.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Tested-by: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-mq-sched.c | 17 +++++++++++++----
block/blk-mq.c | 36 +++++++++++++++++++++++++-----------
block/blk-mq.h | 25 +++++++++++++++++++++----
drivers/scsi/scsi_lib.c | 16 +++++++++++-----
include/linux/blk-mq.h | 4 ++--
5 files changed, 72 insertions(+), 26 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index d1eafe2c045c..bf046530ed4c 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -131,6 +131,7 @@ static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)

do {
struct request *rq;
+ int budget_token;

if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
break;
@@ -140,12 +141,13 @@ static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
break;
}

- if (!blk_mq_get_dispatch_budget(q))
+ budget_token = blk_mq_get_dispatch_budget(q);
+ if (budget_token < 0)
break;

rq = e->type->ops.dispatch_request(hctx);
if (!rq) {
- blk_mq_put_dispatch_budget(q);
+ blk_mq_put_dispatch_budget(q, budget_token);
/*
* We're releasing without dispatching. Holding the
* budget could have blocked any "hctx"s with the
@@ -157,6 +159,8 @@ static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
break;
}

+ blk_mq_set_rq_budget_token(rq, budget_token);
+
/*
* Now this rq owns the budget which has to be released
* if this rq won't be queued to driver via .queue_rq()
@@ -230,6 +234,8 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
struct request *rq;

do {
+ int budget_token;
+
if (!list_empty_careful(&hctx->dispatch)) {
ret = -EAGAIN;
break;
@@ -238,12 +244,13 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
if (!sbitmap_any_bit_set(&hctx->ctx_map))
break;

- if (!blk_mq_get_dispatch_budget(q))
+ budget_token = blk_mq_get_dispatch_budget(q);
+ if (budget_token < 0)
break;

rq = blk_mq_dequeue_from_ctx(hctx, ctx);
if (!rq) {
- blk_mq_put_dispatch_budget(q);
+ blk_mq_put_dispatch_budget(q, budget_token);
/*
* We're releasing without dispatching. Holding the
* budget could have blocked any "hctx"s with the
@@ -255,6 +262,8 @@ static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
break;
}

+ blk_mq_set_rq_budget_token(rq, budget_token);
+
/*
* Now this rq owns the budget which has to be released
* if this rq won't be queued to driver via .queue_rq()
diff --git a/block/blk-mq.c b/block/blk-mq.c
index ae023cf90c30..9e075c333498 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1296,10 +1296,15 @@ static enum prep_dispatch blk_mq_prep_dispatch_rq(struct request *rq,
bool need_budget)
{
struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
+ int budget_token = -1;

- if (need_budget && !blk_mq_get_dispatch_budget(rq->q)) {
- blk_mq_put_driver_tag(rq);
- return PREP_DISPATCH_NO_BUDGET;
+ if (need_budget) {
+ budget_token = blk_mq_get_dispatch_budget(rq->q);
+ if (budget_token < 0) {
+ blk_mq_put_driver_tag(rq);
+ return PREP_DISPATCH_NO_BUDGET;
+ }
+ blk_mq_set_rq_budget_token(rq, budget_token);
}

if (!blk_mq_get_driver_tag(rq)) {
@@ -1316,7 +1321,7 @@ static enum prep_dispatch blk_mq_prep_dispatch_rq(struct request *rq,
* together during handling partial dispatch
*/
if (need_budget)
- blk_mq_put_dispatch_budget(rq->q);
+ blk_mq_put_dispatch_budget(rq->q, budget_token);
return PREP_DISPATCH_NO_TAG;
}
}
@@ -1326,12 +1331,16 @@ static enum prep_dispatch blk_mq_prep_dispatch_rq(struct request *rq,

/* release all allocated budgets before calling to blk_mq_dispatch_rq_list */
static void blk_mq_release_budgets(struct request_queue *q,
- unsigned int nr_budgets)
+ struct list_head *list)
{
- int i;
+ struct request *rq;

- for (i = 0; i < nr_budgets; i++)
- blk_mq_put_dispatch_budget(q);
+ list_for_each_entry(rq, list, queuelist) {
+ int budget_token = blk_mq_get_rq_budget_token(rq);
+
+ if (budget_token >= 0)
+ blk_mq_put_dispatch_budget(q, budget_token);
+ }
}

/*
@@ -1429,7 +1438,8 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED);
bool no_budget_avail = prep == PREP_DISPATCH_NO_BUDGET;

- blk_mq_release_budgets(q, nr_budgets);
+ if (nr_budgets)
+ blk_mq_release_budgets(q, list);

spin_lock(&hctx->lock);
list_splice_tail_init(list, &hctx->dispatch);
@@ -1999,6 +2009,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
{
struct request_queue *q = rq->q;
bool run_queue = true;
+ int budget_token;

/*
* RCU or SRCU read lock is needed before checking quiesced flag.
@@ -2016,11 +2027,14 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
if (q->elevator && !bypass_insert)
goto insert;

- if (!blk_mq_get_dispatch_budget(q))
+ budget_token = blk_mq_get_dispatch_budget(q);
+ if (budget_token < 0)
goto insert;

+ blk_mq_set_rq_budget_token(rq, budget_token);
+
if (!blk_mq_get_driver_tag(rq)) {
- blk_mq_put_dispatch_budget(q);
+ blk_mq_put_dispatch_budget(q, budget_token);
goto insert;
}

diff --git a/block/blk-mq.h b/block/blk-mq.h
index a52703c98b77..bb59a3e54c3b 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -186,17 +186,34 @@ unsigned int blk_mq_in_flight(struct request_queue *q, struct hd_struct *part);
void blk_mq_in_flight_rw(struct request_queue *q, struct hd_struct *part,
unsigned int inflight[2]);

-static inline void blk_mq_put_dispatch_budget(struct request_queue *q)
+static inline void blk_mq_put_dispatch_budget(struct request_queue *q,
+ int budget_token)
{
if (q->mq_ops->put_budget)
- q->mq_ops->put_budget(q);
+ q->mq_ops->put_budget(q, budget_token);
}

-static inline bool blk_mq_get_dispatch_budget(struct request_queue *q)
+static inline int blk_mq_get_dispatch_budget(struct request_queue *q)
{
if (q->mq_ops->get_budget)
return q->mq_ops->get_budget(q);
- return true;
+ return 0;
+}
+
+static inline void blk_mq_set_rq_budget_token(struct request *rq, int token)
+{
+ if (token < 0)
+ return;
+
+ if (rq->q->mq_ops->set_rq_budget_token)
+ rq->q->mq_ops->set_rq_budget_token(rq, token);
+}
+
+static inline int blk_mq_get_rq_budget_token(struct request *rq)
+{
+ if (rq->q->mq_ops->get_rq_budget_token)
+ return rq->q->mq_ops->get_rq_budget_token(rq);
+ return -1;
}

static inline void __blk_mq_inc_active_requests(struct blk_mq_hw_ctx *hctx)
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 022ed2991463..dafcfa3ae77c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -328,6 +328,7 @@ void scsi_device_unbusy(struct scsi_device *sdev, struct scsi_cmnd *cmd)
atomic_dec(&starget->target_busy);

atomic_dec(&sdev->device_busy);
+ cmd->budget_token = -1;
}

static void scsi_kick_queue(struct request_queue *q)
@@ -1138,6 +1139,7 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
unsigned long jiffies_at_alloc;
int retries, to_clear;
bool in_flight;
+ int budget_token = cmd->budget_token;

if (!blk_rq_is_scsi(rq) && !(flags & SCMD_INITIALIZED)) {
flags |= SCMD_INITIALIZED;
@@ -1166,6 +1168,7 @@ void scsi_init_command(struct scsi_device *dev, struct scsi_cmnd *cmd)
cmd->retries = retries;
if (in_flight)
__set_bit(SCMD_STATE_INFLIGHT, &cmd->state);
+ cmd->budget_token = budget_token;

}

@@ -1598,19 +1601,19 @@ static void scsi_mq_done(struct scsi_cmnd *cmd)
blk_mq_complete_request(cmd->request);
}

-static void scsi_mq_put_budget(struct request_queue *q)
+static void scsi_mq_put_budget(struct request_queue *q, int budget_token)
{
struct scsi_device *sdev = q->queuedata;

atomic_dec(&sdev->device_busy);
}

-static bool scsi_mq_get_budget(struct request_queue *q)
+static int scsi_mq_get_budget(struct request_queue *q)
{
struct scsi_device *sdev = q->queuedata;

if (scsi_dev_queue_ready(q, sdev))
- return true;
+ return 0;

atomic_inc(&sdev->restarts);

@@ -1632,7 +1635,7 @@ static bool scsi_mq_get_budget(struct request_queue *q)
if (unlikely(atomic_read(&sdev->device_busy) == 0 &&
!scsi_device_blocked(sdev)))
blk_mq_delay_run_hw_queues(sdev->request_queue, SCSI_QUEUE_DELAY);
- return false;
+ return -1;
}

static void scsi_mq_set_rq_budget_token(struct request *req, int token)
@@ -1660,6 +1663,8 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
blk_status_t ret;
int reason;

+ WARN_ON_ONCE(cmd->budget_token < 0);
+
/*
* If the device is not in running state we will reject some or all
* commands.
@@ -1711,7 +1716,8 @@ static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,
if (scsi_target(sdev)->can_queue > 0)
atomic_dec(&scsi_target(sdev)->target_busy);
out_put_budget:
- scsi_mq_put_budget(q);
+ scsi_mq_put_budget(q, cmd->budget_token);
+ cmd->budget_token = -1;
switch (ret) {
case BLK_STS_OK:
break;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index d2c66b453d07..b2e1b8daf12f 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -309,12 +309,12 @@ struct blk_mq_ops {
* reserved budget. Also we have to handle failure case
* of .get_budget for avoiding I/O deadlock.
*/
- bool (*get_budget)(struct request_queue *);
+ int (*get_budget)(struct request_queue *);

/**
* @put_budget: Release the reserved budget.
*/
- void (*put_budget)(struct request_queue *);
+ void (*put_budget)(struct request_queue *, int);

/*
* @set_rq_budget_toekn: store rq's budget token
--
2.25.4