On Wed, Aug 18, 2021 at 10:38:15AM +0100, John Garry wrote: > On 22/07/2021 10:52, Ming Lei wrote: > > blk-mq deactivates one hctx when the last CPU in hctx->cpumask become > > offline by draining all requests originated from this hctx and moving new > > allocation to other active hctx. This way is for avoiding inflight IO in > > case of managed irq because managed irq is shutdown when the last CPU in > > the irq's affinity becomes offline. > > > > However, lots of drivers(nvme fc, rdma, tcp, loop, ...) don't use managed > > irq, so they needn't to deactivate hctx when the last CPU becomes offline. > > Also, some of them are the only user of blk_mq_alloc_request_hctx() which > > is used for connecting io queue. And their requirement is that the connect > > request needs to be submitted successfully via one specified hctx even though > > all CPUs in this hctx->cpumask have become offline. > > > > Addressing the requirement for nvme fc/rdma/loop by allowing to > > allocate request from one hctx when all CPUs in this hctx are offline, > > since these drivers don't use managed irq. > > > > Finally don't deactivate one hctx when it doesn't use managed irq. > > > > Reviewed-by: Christoph Hellwig<hch@xxxxxx> > > Signed-off-by: Ming Lei<ming.lei@xxxxxxxxxx> > > Sorry for lateness. Just a few minor comments below, regardless: > > Reviewed-by: John Garry <john.garry@xxxxxxxxxx> > > > --- > > block/blk-mq.c | 27 +++++++++++++++++---------- > > block/blk-mq.h | 8 ++++++++ > > 2 files changed, 25 insertions(+), 10 deletions(-) > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > index 2c4ac51e54eb..591ab07c64d8 100644 > > --- a/block/blk-mq.c > > +++ b/block/blk-mq.c > > @@ -427,6 +427,15 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op, > > } > > EXPORT_SYMBOL(blk_mq_alloc_request); > > +static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx) > > I don't see why it needs to be inline. I think generally we leave it to the > compiler to decide. Usually if one function is called more than two times, it will not be inlined. blk_mq_first_mapped_cpu() is called in fast path, so we need to inline it. > > > +{ > > + int cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask); > > + > > + if (cpu >= nr_cpu_ids) > > + cpu = cpumask_first(hctx->cpumask); > > + return cpu; > > +} > > + > > struct request *blk_mq_alloc_request_hctx(struct request_queue *q, > > unsigned int op, blk_mq_req_flags_t flags, unsigned int hctx_idx) > > { > > @@ -468,7 +477,10 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q, > > data.hctx = q->queue_hw_ctx[hctx_idx]; > > if (!blk_mq_hw_queue_mapped(data.hctx)) > > goto out_queue_exit; > > - cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask); > > + > > + WARN_ON_ONCE(blk_mq_hctx_use_managed_irq(data.hctx)); > > + > > + cpu = blk_mq_first_mapped_cpu(data.hctx); > > data.ctx = __blk_mq_get_ctx(q, cpu); > > if (!q->elevator) > > @@ -1501,15 +1513,6 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) > > hctx_unlock(hctx, srcu_idx); > > } > > -static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx) > > -{ > > - int cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask); > > - > > - if (cpu >= nr_cpu_ids) > > - cpu = cpumask_first(hctx->cpumask); > > - return cpu; > > -} > > - > > /* > > * It'd be great if the workqueue API had a way to pass > > * in a mask and had some smarts for more clever placement. > > @@ -2556,6 +2559,10 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node) > > struct blk_mq_hw_ctx *hctx = hlist_entry_safe(node, > > struct blk_mq_hw_ctx, cpuhp_online); > > + /* hctx needn't to be deactivated in case managed irq isn't used */ > > + if (!blk_mq_hctx_use_managed_irq(hctx)) > > + return 0; > > In a previous version (v2) I think that we just didn't register the cpu > hotplug handlers, so not sure why that changed. Sorry, forget to mention the change, inside blk_mq_realloc_hw_ctxs() we may grab one cached hctx without initializing it, so use managed irq info change may not be visible in blk_mq_init_hctx(). Given blk_mq_hctx_notify_offline() isn't in fast path, I'd rather to check in blk_mq_hctx_notify_offline(), which is more reliable than running the check in blk_mq_init_hctx(). > > > + > > if (!cpumask_test_cpu(cpu, hctx->cpumask) || > > !blk_mq_last_cpu_in_hctx(cpu, hctx)) > > return 0; > > diff --git a/block/blk-mq.h b/block/blk-mq.h > > index d08779f77a26..7333b659d8f5 100644 > > --- a/block/blk-mq.h > > +++ b/block/blk-mq.h > > @@ -119,6 +119,14 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q, > > return ctx->hctxs[type]; > > } > > +static inline bool blk_mq_hctx_use_managed_irq(struct blk_mq_hw_ctx *hctx) > > +{ > > + if (hctx->type == HCTX_TYPE_POLL) > > + return false; > > + > > + return hctx->queue->tag_set->map[hctx->type].use_managed_irq; > > +} > > This function only seems to be used in blk-mq.c, so not sure why you put it > in .h file. oops, the helper must be used in early version, I will send a new version soon. Thanks, Ming