On 8/12/19 3:43 PM, Ming Lei wrote:
> When all CPUs in one hctx are offline, we shouldn't run this hw queue
> for completing request any more.
>
> So steal bios from the request, and resubmit them, and finally free
> the request in blk_mq_hctx_notify_dead().
>
> Cc: Bart Van Assche <bvanassche@xxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq.c | 48 +++++++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 41 insertions(+), 7 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 6931b2ba2776..ed334fd867c4 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2261,10 +2261,30 @@ static int blk_mq_hctx_notify_online(unsigned int cpu, struct hlist_node *node)
> return 0;
> }
>
> +static void blk_mq_resubmit_io(struct request *rq)
> +{
> + struct bio_list list;
> + struct bio *bio;
> +
> + bio_list_init(&list);
> + blk_steal_bios(&list, rq);
> +
> + while (true) {
> + bio = bio_list_pop(&list);
> + if (!bio)
> + break;
> +
> + generic_make_request(bio);
> + }
> +
> + blk_mq_cleanup_rq(rq);
> + blk_mq_end_request(rq, 0);
> +}
> +
> /*
> - * 'cpu' is going away. splice any existing rq_list entries from this
> - * software queue to the hw queue dispatch list, and ensure that it
> - * gets run.
> + * 'cpu' has gone away. If this hctx is dead, we can't dispatch request
> + * to the hctx any more, so steal bios from requests of this hctx, and
> + * re-submit them to the request queue, and free these requests finally.
> */
> static int blk_mq_hctx_notify_dead(unsigned int cpu, struct hlist_node *node)
> {
> @@ -2272,6 +2292,8 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu, struct hlist_node *node)
> struct blk_mq_ctx *ctx;
> LIST_HEAD(tmp);
> enum hctx_type type;
> + bool hctx_dead;
> + struct request *rq;
>
> hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp_dead);
> ctx = __blk_mq_get_ctx(hctx->queue, cpu);
> @@ -2279,6 +2301,9 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu, struct hlist_node *node)
>
> clear_bit(BLK_MQ_S_INTERNAL_STOPPED, &hctx->state);
>
> + hctx_dead = cpumask_first_and(hctx->cpumask, cpu_online_mask) >=
> + nr_cpu_ids;
> +
> spin_lock(&ctx->lock);
> if (!list_empty(&ctx->rq_lists[type])) {
> list_splice_init(&ctx->rq_lists[type], &tmp);
> @@ -2289,11 +2314,20 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu, struct hlist_node *node)
> if (list_empty(&tmp))
> return 0;
>
> - spin_lock(&hctx->lock);
> - list_splice_tail_init(&tmp, &hctx->dispatch);
> - spin_unlock(&hctx->lock);
> + if (!hctx_dead) {
> + spin_lock(&hctx->lock);
> + list_splice_tail_init(&tmp, &hctx->dispatch);
> + spin_unlock(&hctx->lock);
> + blk_mq_run_hw_queue(hctx, true);
> + return 0;
> + }
> +
> + while (!list_empty(&tmp)) {
> + rq = list_entry(tmp.next, struct request, queuelist);
> + list_del_init(&rq->queuelist);
> + blk_mq_resubmit_io(rq);
> + }
>
> - blk_mq_run_hw_queue(hctx, true);
> return 0;
> }
>
>
So what happens when all CPUs assigned to a hardware queue go offline?
Wouldn't blk_steal_bios() etc resend the I/O to the same hw queue,
causing an infinite loop?
Don't we have to rearrange the hardware queues here?
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)
