Some drivers, for example of mtip32xx, use the 'request_index'
passed to .init_request() as hardware tag index for initializing
hardware queue, and these drivers actually require that rq->tag
is always same with 'request_index' passed to .init_request().
After blk-mq I/O scheduler is in, the driver tag is allocated
during dispatching, and the allocated driver tag can't be same
with I/O scheduler's tag, so blk-mq I/O scheduler breaks these
devices, like mtip32xx.
This patch introduces BLK_MQ_F_SCHED_USE_HW_TAG flag, and just
allocate hardware tag for scheduler directly, then we can address
mtip32xx's issue.
On the other hand, this feature should make blk-mq io scheduler
more efficient than current way if the hardware tag space is big
enough, because we can save one tag allocation/release.
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
block/blk-mq-sched.c | 10 +++++++++-
block/blk-mq.c | 35 +++++++++++++++++++++++++++++------
include/linux/blk-mq.h | 1 +
3 files changed, 39 insertions(+), 7 deletions(-)
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 9e3c0f92851b..1ff4b61135bc 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -83,7 +83,12 @@ struct request *blk_mq_sched_get_request(struct request_queue *q,
data->hctx = blk_mq_map_queue(q, data->ctx->cpu);
if (e) {
- data->flags |= BLK_MQ_REQ_INTERNAL;
+ /*
+ * If BLK_MQ_F_SCHED_USE_HW_TAG is set, we use hardware
+ * tag as scheduler tag.
+ */
+ if (!(data->hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG))
+ data->flags |= BLK_MQ_REQ_INTERNAL;
/*
* Flush requests are special and go directly to the
@@ -445,6 +450,9 @@ static int blk_mq_sched_alloc_tags(struct request_queue *q,
struct blk_mq_tag_set *set = q->tag_set;
int ret;
+ if (hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG)
+ return 0;
+
hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
set->reserved_tags);
if (!hctx->sched_tags)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index e536dacfae4c..ac6245bdbc8c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -247,9 +247,19 @@ struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data,
rq->rq_flags = RQF_MQ_INFLIGHT;
atomic_inc(&data->hctx->nr_active);
}
- rq->tag = tag;
- rq->internal_tag = -1;
- data->hctx->tags->rqs[rq->tag] = rq;
+ data->hctx->tags->rqs[tag] = rq;
+
+ /*
+ * If we use hw tag for scheduling, postpone setting
+ * rq->tag in blk_mq_get_driver_tag().
+ */
+ if (data->hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG) {
+ rq->tag = -1;
+ rq->internal_tag = tag;
+ } else {
+ rq->tag = tag;
+ rq->internal_tag = -1;
+ }
}
blk_mq_rq_ctx_init(data->q, data->ctx, rq, op);
@@ -349,7 +359,7 @@ void __blk_mq_finish_request(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
clear_bit(REQ_ATOM_POLL_SLEPT, &rq->atomic_flags);
if (rq->tag != -1)
blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag);
- if (sched_tag != -1)
+ if (sched_tag != -1 && !(hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG))
blk_mq_sched_completed_request(hctx, rq);
blk_mq_sched_restart(hctx);
blk_queue_exit(q);
@@ -866,6 +876,12 @@ bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
if (rq->tag != -1)
goto done;
+ /* we buffered driver tag in rq->internal_tag */
+ if (data.hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG) {
+ rq->tag = rq->internal_tag;
+ goto done;
+ }
+
if (blk_mq_tag_is_reserved(data.hctx->sched_tags, rq->internal_tag))
data.flags |= BLK_MQ_REQ_RESERVED;
@@ -887,9 +903,15 @@ bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
static void __blk_mq_put_driver_tag(struct blk_mq_hw_ctx *hctx,
struct request *rq)
{
- blk_mq_put_tag(hctx, hctx->tags, rq->mq_ctx, rq->tag);
+ unsigned tag = rq->tag;
+
rq->tag = -1;
+ if (hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG)
+ return;
+
+ blk_mq_put_tag(hctx, hctx->tags, rq->mq_ctx, tag);
+
if (rq->rq_flags & RQF_MQ_INFLIGHT) {
rq->rq_flags &= ~RQF_MQ_INFLIGHT;
atomic_dec(&hctx->nr_active);
@@ -2852,7 +2874,8 @@ bool blk_mq_poll(struct request_queue *q, blk_qc_t cookie)
blk_flush_plug_list(plug, false);
hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
- if (!blk_qc_t_is_internal(cookie))
+ if (!blk_qc_t_is_internal(cookie) || (hctx->flags &
+ BLK_MQ_F_SCHED_USE_HW_TAG))
rq = blk_mq_tag_to_rq(hctx->tags, blk_qc_t_to_tag(cookie));
else
rq = blk_mq_tag_to_rq(hctx->sched_tags, blk_qc_t_to_tag(cookie));
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index b90c3d5766cd..be605a05f340 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -154,6 +154,7 @@ enum {
BLK_MQ_F_SG_MERGE = 1 << 2,
BLK_MQ_F_BLOCKING = 1 << 5,
BLK_MQ_F_NO_SCHED = 1 << 6,
+ BLK_MQ_F_SCHED_USE_HW_TAG = 1 << 7,
BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
BLK_MQ_F_ALLOC_POLICY_BITS = 1,
--
2.9.3
