This function is introduced for dequeuing request
from sw queue so that we can dispatch it in
scheduler's way.
More importantly, some SCSI devices may set
q->queue_depth, which is a per-request_queue limit,
and applied on pending I/O from all hctxs. This
function is introduced for avoiding to dequeue too
many requests from sw queue when ->dispatch isn't
flushed completely.
Tested-by: Oleksandr Natalenko <oleksa...@natalenko.name>
Tested-by: Tom Nguyen <tom81...@gmail.com>
Tested-by: Paolo Valente <paolo.vale...@linaro.org>
Reviewed-by: Bart Van Assche <bart.vanass...@wdc.com>
Signed-off-by: Ming Lei <ming....@redhat.com>
---
block/blk-mq.c | 38 ++++++++++++++++++++++++++++++++++++++
block/blk-mq.h | 2 ++
2 files changed, 40 insertions(+)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index d1b9fb539eba..8b49af1ade7f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -882,6 +882,44 @@ void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx,
struct list_head *list)
}
EXPORT_SYMBOL_GPL(blk_mq_flush_busy_ctxs);
+struct dispatch_rq_data {
+ struct blk_mq_hw_ctx *hctx;
+ struct request *rq;
+};
+
+static bool dispatch_rq_from_ctx(struct sbitmap *sb, unsigned int bitnr, void
*data)
+{
+ struct dispatch_rq_data *dispatch_data = data;
+ struct blk_mq_hw_ctx *hctx = dispatch_data->hctx;
+ struct blk_mq_ctx *ctx = hctx->ctxs[bitnr];
+
+ spin_lock(&ctx->lock);
+ if (unlikely(!list_empty(&ctx->rq_list))) {
+ dispatch_data->rq = list_entry_rq(ctx->rq_list.next);
+ list_del_init(&dispatch_data->rq->queuelist);
+ if (list_empty(&ctx->rq_list))
+ sbitmap_clear_bit(sb, bitnr);
+ }
+ spin_unlock(&ctx->lock);
+
+ return !dispatch_data->rq;
+}
+
+struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,
+ struct blk_mq_ctx *start)
+{
+ unsigned off = start ? start->index_hw : 0;
+ struct dispatch_rq_data data = {
+ .hctx = hctx,
+ .rq = NULL,
+ };
+
+ __sbitmap_for_each_set(&hctx->ctx_map, off,
+ dispatch_rq_from_ctx, &data);
+
+ return data.rq;
+}
+
static inline unsigned int queued_to_index(unsigned int queued)
{
if (!queued)
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 61aecf398a4b..915de58572e7 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -35,6 +35,8 @@ void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx,
struct list_head *list);
bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx);
bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
bool wait);
+struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,
+ struct blk_mq_ctx *start);
/*
* Internal helpers for allocating/freeing the request map
--
2.9.5
