On Tue, Jul 16, 2019 at 11:03:14AM +0800, John Garry wrote:
> 在 12/07/2019 10:47, Ming Lei 写道:
> > Most of blk-mq drivers depend on managed IRQ's auto-affinity to setup
> > up queue mapping. Thomas mentioned the following point[1]:
> >
> > "
> > That was the constraint of managed interrupts from the very beginning:
> >
> > The driver/subsystem has to quiesce the interrupt line and the associated
> > queue _before_ it gets shutdown in CPU unplug and not fiddle with it
> > until it's restarted by the core when the CPU is plugged in again.
> > "
> >
> > However, current blk-mq implementation doesn't quiesce hw queue before
> > the last CPU in the hctx is shutdown. Even worse, CPUHP_BLK_MQ_DEAD is
> > one cpuhp state handled after the CPU is down, so there isn't any chance
> > to quiesce hctx for blk-mq wrt. CPU hotplug.
> >
> > Add new cpuhp state of CPUHP_AP_BLK_MQ_ONLINE for blk-mq to stop queues
> > and wait for completion of in-flight requests.
> >
> > [1]
> > https://lore.kernel.org/linux-block/alpine.deb.2.21.1904051331270.1...@nanos.tec.linutronix.de/
> >
> > Cc: Bart Van Assche <bvanass...@acm.org>
> > Cc: Hannes Reinecke <h...@suse.com>
> > Cc: Christoph Hellwig <h...@lst.de>
> > Cc: Thomas Gleixner <t...@linutronix.de>
> > Cc: Keith Busch <keith.bu...@intel.com>
> > Signed-off-by: Ming Lei <ming....@redhat.com>
> > ---
> > block/blk-mq-tag.c | 2 +-
> > block/blk-mq-tag.h | 2 ++
> > block/blk-mq.c | 67 ++++++++++++++++++++++++++++++++++++++
> > include/linux/blk-mq.h | 1 +
> > include/linux/cpuhotplug.h | 1 +
> > 5 files changed, 72 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
> > index da19f0bc8876..bcefb213ad69 100644
> > --- a/block/blk-mq-tag.c
> > +++ b/block/blk-mq-tag.c
> > @@ -324,7 +324,7 @@ static void bt_tags_for_each(struct blk_mq_tags *tags,
> > struct sbitmap_queue *bt,
> > * true to continue iterating tags, false to stop.
> > * @priv: Will be passed as second argument to @fn.
> > */
> > -static void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
> > +void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
> > busy_tag_iter_fn *fn, void *priv)
> > {
> > if (tags->nr_reserved_tags)
> > diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
> > index 61deab0b5a5a..321fd6f440e6 100644
> > --- a/block/blk-mq-tag.h
> > +++ b/block/blk-mq-tag.h
> > @@ -35,6 +35,8 @@ extern int blk_mq_tag_update_depth(struct blk_mq_hw_ctx
> > *hctx,
> > extern void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool);
> > void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
> > void *priv);
> > +void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
> > + busy_tag_iter_fn *fn, void *priv);
> > static inline struct sbq_wait_state *bt_wait_ptr(struct sbitmap_queue *bt,
> > struct blk_mq_hw_ctx *hctx)
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index e5ef40c603ca..028c5d78e409 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -2205,6 +2205,64 @@ int blk_mq_alloc_rqs(struct blk_mq_tag_set *set,
> > struct blk_mq_tags *tags,
> > return -ENOMEM;
> > }
> > +static bool blk_mq_count_inflight_rq(struct request *rq, void *data,
> > + bool reserved)
> > +{
> > + unsigned *count = data;
> > +
> > + if ((blk_mq_rq_state(rq) == MQ_RQ_IN_FLIGHT))
> > + (*count)++;
> > +
> > + return true;
> > +}
> > +
> > +unsigned blk_mq_tags_inflight_rqs(struct blk_mq_tags *tags)
> > +{
> > + unsigned count = 0;
> > +
> > + blk_mq_all_tag_busy_iter(tags, blk_mq_count_inflight_rq, &count);
> > +
> > + return count;
> > +}
> > +
> > +static void blk_mq_drain_inflight_rqs(struct blk_mq_hw_ctx *hctx)
> > +{
> > + while (1) {
> > + if (!blk_mq_tags_inflight_rqs(hctx->tags))
> > + break;
> > + msleep(5);
> > + }
> > +}
> > +
> > +static int blk_mq_hctx_notify_online(unsigned int cpu, struct hlist_node
> > *node)
> > +{
> > + struct blk_mq_hw_ctx *hctx = hlist_entry_safe(node,
> > + struct blk_mq_hw_ctx, cpuhp_online);
> > + unsigned prev_cpu = -1;
> > +
> > + if (hctx->flags & BLK_MQ_F_NO_MANAGED_IRQ)
> > + return 0;
>
> is it possible to make this check at registration, such that we don't even
> register for when (hctx->flags & BLK_MQ_F_NO_MANAGED_IRQ)?
Yeah, good idea, it can be done in that way.
>
> > +
> > + while (true) {
> > + unsigned other_cpu = cpumask_next_and(prev_cpu, hctx->cpumask,
>
> nit: to me name next_cpu seems better
OK.
>
> > + cpu_online_mask);
> > +
> > + if (other_cpu >= nr_cpu_ids)
> > + break;
> > +
> > + /* return if there is other online CPU on this hctx */
> > + if (other_cpu != cpu)
> > + return 0;
> > +
> > + prev_cpu = other_cpu;
> > + }
> > +
> > + set_bit(BLK_MQ_S_INTERNAL_STOPPED, &hctx->state);
> > + blk_mq_drain_inflight_rqs(hctx);
> > +
> > + return 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
> > @@ -2221,6 +2279,9 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu,
> > struct hlist_node *node)
> > ctx = __blk_mq_get_ctx(hctx->queue, cpu);
> > type = hctx->type;
> > + if (test_bit(BLK_MQ_S_INTERNAL_STOPPED, &hctx->state))
> > + clear_bit(BLK_MQ_S_INTERNAL_STOPPED, &hctx->state);
>
> can you just always clear the bit without the test?
Yeah.
>
> > +
> > spin_lock(&ctx->lock);
> > if (!list_empty(&ctx->rq_lists[type])) {
> > list_splice_init(&ctx->rq_lists[type], &tmp);
> > @@ -2243,6 +2304,8 @@ static void blk_mq_remove_cpuhp(struct blk_mq_hw_ctx
> > *hctx)
> > {
> > cpuhp_state_remove_instance_nocalls(CPUHP_BLK_MQ_DEAD,
> > &hctx->cpuhp_dead);
> > + cpuhp_state_remove_instance_nocalls(CPUHP_AP_BLK_MQ_ONLINE,
> > + &hctx->cpuhp_online);
> > }
> > /* hctx->ctxs will be freed in queue's release handler */
> > @@ -2301,6 +2364,8 @@ static int blk_mq_init_hctx(struct request_queue *q,
> > hctx->queue_num = hctx_idx;
> > cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_DEAD, &hctx->cpuhp_dead);
> > + cpuhp_state_add_instance_nocalls(CPUHP_AP_BLK_MQ_ONLINE,
> > + &hctx->cpuhp_online);
> > hctx->tags = set->tags[hctx_idx];
> > @@ -3536,6 +3601,8 @@ static int __init blk_mq_init(void)
> > {
> > cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL,
> > blk_mq_hctx_notify_dead);
> > + cpuhp_setup_state_multi(CPUHP_AP_BLK_MQ_ONLINE, "block/mq:online",
> > + NULL, blk_mq_hctx_notify_online);
> > return 0;
> > }
> > subsys_initcall(blk_mq_init);
> > diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> > index 911cdc6479dc..dc86bdac08f4 100644
> > --- a/include/linux/blk-mq.h
> > +++ b/include/linux/blk-mq.h
> > @@ -59,6 +59,7 @@ struct blk_mq_hw_ctx {
> > atomic_t nr_active;
> > struct hlist_node cpuhp_dead;
> > + struct hlist_node cpuhp_online;
>
> I'd reorder with cpuhp_dead
Fine.
thanks,
Ming
