[PATCH 2/2] blk-mq: simplify queue mapping & schedule with each possisble CPU

Ming Lei
2018-01-12T02:54:07Z

From: Christoph Hellwig <hch@lst.de>

The previous patch assigns interrupt vectors to all possible CPUs, so
now hctx can be mapped to possible CPUs, this patch applies this fact
to simplify queue mapping & schedule so that we don't need to handle
CPU hotplug for dealing with physical CPU plug & unplug. With this
simplication, we can work well on physical CPU plug & unplug, which
is a normal use case for VM at least.

Make sure we allocate blk_mq_ctx structures for all possible CPUs, and
set hctx->numa_node for possible CPUs which are mapped to this hctx. And
only choose the online CPUs for schedule.

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Stefan Haberland <sth@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
(merged the three into one because any single one may not work, and fix
selecting online CPUs for scheduler)
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
block/blk-mq.c | 19 ++++++++-----------
1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8000ba6db07d..ef9beca2d117 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -440,7 +440,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
blk_queue_exit(q);
return ERR_PTR(-EXDEV);
}
- cpu = cpumask_first(alloc_data.hctx->cpumask);
+ cpu = cpumask_first_and(alloc_data.hctx->cpumask, cpu_online_mask);
alloc_data.ctx = __blk_mq_get_ctx(q, cpu);

rq = blk_mq_get_request(q, NULL, op, &alloc_data);
@@ -1323,9 +1323,10 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
if (--hctx->next_cpu_batch <= 0) {
int next_cpu;

- next_cpu = cpumask_next(hctx->next_cpu, hctx->cpumask);
+ next_cpu = cpumask_next_and(hctx->next_cpu, hctx->cpumask,
+ cpu_online_mask);
if (next_cpu >= nr_cpu_ids)
- next_cpu = cpumask_first(hctx->cpumask);
+ next_cpu = cpumask_first_and(hctx->cpumask,cpu_online_mask);

hctx->next_cpu = next_cpu;
hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
@@ -2219,16 +2220,11 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
INIT_LIST_HEAD(&__ctx->rq_list);
__ctx->queue = q;

- /* If the cpu isn't present, the cpu is mapped to first hctx */
- if (!cpu_present(i))
- continue;
-
- hctx = blk_mq_map_queue(q, i);
-
/*
* Set local node, IFF we have more than one hw queue. If
* not, we remain on the home node of the device
*/
+ hctx = blk_mq_map_queue(q, i);
if (nr_hw_queues > 1 && hctx->numa_node == NUMA_NO_NODE)
hctx->numa_node = local_memory_node(cpu_to_node(i));
}
@@ -2285,7 +2281,7 @@ static void blk_mq_map_swqueue(struct request_queue *q)
*
* If the cpu isn't present, the cpu is mapped to first hctx.
*/
- for_each_present_cpu(i) {
+ for_each_possible_cpu(i) {
hctx_idx = q->mq_map[i];
/* unmapped hw queue can be remapped after CPU topo changed */
if (!set->tags[hctx_idx] &&
@@ -2339,7 +2335,8 @@ static void blk_mq_map_swqueue(struct request_queue *q)
/*
* Initialize batch roundrobin counts
*/
- hctx->next_cpu = cpumask_first(hctx->cpumask);
+ hctx->next_cpu = cpumask_first_and(hctx->cpumask,
+ cpu_online_mask);
hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
}
}
--
2.9.5