On Mon, Jul 27, 2020 at 04:10:21PM -0700, Sagi Grimberg wrote:
> drivers that have shared tagsets may need to quiesce potentially a lot
> of request queues that all share a single tagset (e.g. nvme). Add an interface
> to quiesce all the queues on a given tagset. This interface is useful because
> it can speedup the quiesce by doing it in parallel.
>
> For tagsets that have BLK_MQ_F_BLOCKING set, we use call_srcu to all hctxs
> in parallel such that all of them wait for the same rcu elapsed period with
> a per-hctx heap allocated rcu_synchronize. for tagsets that don't have
> BLK_MQ_F_BLOCKING set, we simply call a single synchronize_rcu as this is
> sufficient.
>
> Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
> ---
> block/blk-mq.c | 66 ++++++++++++++++++++++++++++++++++++++++++
> include/linux/blk-mq.h | 4 +++
> 2 files changed, 70 insertions(+)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index abcf590f6238..c37e37354330 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -209,6 +209,42 @@ void blk_mq_quiesce_queue_nowait(struct request_queue *q)
> }
> EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
>
> +static void blk_mq_quiesce_blocking_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) {
> + WARN_ON_ONCE(!(hctx->flags & BLK_MQ_F_BLOCKING));
> + hctx->rcu_sync = kmalloc(sizeof(*hctx->rcu_sync), GFP_KERNEL);
> + if (!hctx->rcu_sync)
> + continue;
This approach of quiesce/unquiesce tagset is good abstraction.
Just one more thing, please allocate a rcu_sync array because hctx is supposed
to not store scratch stuff.
thanks,
Ming
