Hi Sagi,
On Sat, Jul 25, 2020 at 05:23:00PM -0700, Sagi Grimberg wrote:
> Drivers that may have to quiesce a large amount of request queues at once
> (e.g. controller or adapter reset). These drivers would benefit from an
> async quiesce interface such that the can trigger quiesce asynchronously
> and wait for all in parallel.
>
> This leaves the synchronization responsibility to the driver, but adds
> a convenient interface to quiesce async and wait in a single pass.
>
> Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
> ---
> block/blk-mq.c | 32 ++++++++++++++++++++++++++++++++
> include/linux/blk-mq.h | 4 ++++
> 2 files changed, 36 insertions(+)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index abcf590f6238..60d137265bd9 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -209,6 +209,38 @@ void blk_mq_quiesce_queue_nowait(struct request_queue *q)
> }
> EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
>
> +void blk_mq_quiesce_queue_async(struct request_queue *q)
> +{
> + struct blk_mq_hw_ctx *hctx;
> + unsigned int i;
> +
> + blk_mq_quiesce_queue_nowait(q);
> +
> + queue_for_each_hw_ctx(q, hctx, i) {
> + init_completion(&hctx->rcu_sync.completion);
> + init_rcu_head(&hctx->rcu_sync.head);
> + if (hctx->flags & BLK_MQ_F_BLOCKING)
> + call_srcu(hctx->srcu, &hctx->rcu_sync.head,
> + wakeme_after_rcu);
> + else
> + call_rcu(&hctx->rcu_sync.head,
> + wakeme_after_rcu);
> + }
Looks not necessary to do anything in case of !BLK_MQ_F_BLOCKING, and single
synchronize_rcu() is OK for all hctx during waiting.
> +}
> +EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_async);
> +
> +void blk_mq_quiesce_queue_async_wait(struct request_queue *q)
> +{
> + struct blk_mq_hw_ctx *hctx;
> + unsigned int i;
> +
> + queue_for_each_hw_ctx(q, hctx, i) {
> + wait_for_completion(&hctx->rcu_sync.completion);
> + destroy_rcu_head(&hctx->rcu_sync.head);
> + }
> +}
> +EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_async_wait);
> +
> /**
> * blk_mq_quiesce_queue() - wait until all ongoing dispatches have finished
> * @q: request queue.
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 23230c1d031e..5536e434311a 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -5,6 +5,7 @@
> #include <linux/blkdev.h>
> #include <linux/sbitmap.h>
> #include <linux/srcu.h>
> +#include <linux/rcupdate_wait.h>
>
> struct blk_mq_tags;
> struct blk_flush_queue;
> @@ -170,6 +171,7 @@ struct blk_mq_hw_ctx {
> */
> struct list_head hctx_list;
>
> + struct rcu_synchronize rcu_sync;
The above struct takes at least 5 words, and I'd suggest to avoid it,
and the hctx->srcu should be re-used for waiting BLK_MQ_F_BLOCKING.
Meantime !BLK_MQ_F_BLOCKING doesn't need it.
Thanks,
Ming
