Re: [PATCH V2 RESEND 3/5] blk-mq: stop to handle IO before hctx's all CPUs become offline

[Ming Lei <ming.lei@redhat.com>]

On Mon, Oct 07, 2019 at 11:23:22AM +0100, John Garry wrote:
> On 06/10/2019 03:45, Ming Lei wrote:
> > +	}
> > +}
> > +
> > +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;
> > +
> > +	while (true) {
> > +		unsigned next_cpu = cpumask_next_and(prev_cpu, hctx->cpumask,
> > +				cpu_online_mask);
> > +
> > +		if (next_cpu >= nr_cpu_ids)
> > +			break;
> > +
> > +		/* return if there is other online CPU on this hctx */
> > +		if (next_cpu != cpu)
> > +			return 0;
> > +
> > +		prev_cpu = next_cpu;
> > +	}
> > +
> > +	set_bit(BLK_MQ_S_INTERNAL_STOPPED, &hctx->state);
> > +	blk_mq_drain_inflight_rqs(hctx);
> > +
> 
> Does this do the same:
> 
> {
> 	struct blk_mq_hw_ctx *hctx = hlist_entry_safe(node,
> 			struct blk_mq_hw_ctx, cpuhp_online);
> 	cpumask_var_t tmp;
> 
> 	cpumask_and(tmp, hctx->cpumask, cpu_online_mask);
> 
> 	/* test if there is any other cpu online in the hctx cpu mask */
> 	if (cpumask_any_but(tmp, cpu) < nr_cpu_ids)
> 		return 0;
> 
> 	set_bit(BLK_MQ_S_INTERNAL_STOPPED, &hctx->state);
> 	blk_mq_drain_inflight_rqs(hctx);
> 
> 	return 0;
> }
> 
> If so, it's more readable and concise.

Yes, but we have to allocate space for 'tmp', that is what this patch
tries to avoid, given the logic isn't too complicated.

> 
> 
> BTW, You could have added my Tested-by tags...

OK, I will add it in V3.


Thanks,
Ming