[PATCH 1/8] blk-mq: make sure that correct hctx->next_cpu is set

[PATCH 1/8] blk-mq: make sure that correct hctx->next_cpu is set

[Ming Lei]

>From commit 20e4d81393196 (blk-mq: simplify queue mapping & schedule
with each possisble CPU), one hctx can be mapped from all offline CPUs,
then hctx->next_cpu can be set as wrong.

This patch fixes this issue by making hctx->next_cpu pointing to the
first CPU in hctx->cpumask if all CPUs in hctx->cpumask are offline.

Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
Fixes: 20e4d81393196 ("blk-mq: simplify queue mapping & schedule with each possisble CPU")
Cc: stable@vger.kernel.org
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f5c7dbcb954f..9b220dc415ac 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2432,6 +2432,8 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 		 */
 		hctx->next_cpu = cpumask_first_and(hctx->cpumask,
 				cpu_online_mask);
+		if (hctx->next_cpu >= nr_cpu_ids)
+			hctx->next_cpu = cpumask_first(hctx->cpumask);
 		hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
 	}
 }
-- 
2.9.5

Re: [PATCH 1/8] blk-mq: make sure that correct hctx->next_cpu is set

[Christoph Hellwig]

On Sun, Apr 08, 2018 at 05:48:07PM +0800, Ming Lei wrote:
> >From commit 20e4d81393196 (blk-mq: simplify queue mapping & schedule
> with each possisble CPU), one hctx can be mapped from all offline CPUs,
> then hctx->next_cpu can be set as wrong.
> 
> This patch fixes this issue by making hctx->next_cpu pointing to the
> first CPU in hctx->cpumask if all CPUs in hctx->cpumask are offline.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 1/8] blk-mq: make sure that correct hctx->next_cpu is set

[Sagi Grimberg]

Looks good,

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

[PATCH 2/8] blk-mq: don't keep offline CPUs mapped to hctx 0

[Ming Lei]

>From commit 4b855ad37194 ("blk-mq: Create hctx for each present CPU),
blk-mq doesn't remap queue after CPU topo is changed, that said when
some of these offline CPUs become online, they are still mapped to
hctx 0, then hctx 0 may become the bottleneck of IO dispatch and
completion.

This patch sets up the mapping from the beginning, and aligns to
queue mapping for PCI device (blk_mq_pci_map_queues()).

Fixes: 4b855ad37194 ("blk-mq: Create hctx for each present CPU)
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-cpumap.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 9f8cffc8a701..3eb169f15842 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -16,11 +16,6 @@
 
 static int cpu_to_queue_index(unsigned int nr_queues, const int cpu)
 {
-	/*
-	 * Non present CPU will be mapped to queue index 0.
-	 */
-	if (!cpu_present(cpu))
-		return 0;
 	return cpu % nr_queues;
 }
 
-- 
2.9.5

Re: [PATCH 2/8] blk-mq: don't keep offline CPUs mapped to hctx 0

[Christoph Hellwig]

On Sun, Apr 08, 2018 at 05:48:08PM +0800, Ming Lei wrote:
> >From commit 4b855ad37194 ("blk-mq: Create hctx for each present CPU),
> blk-mq doesn't remap queue after CPU topo is changed, that said when
> some of these offline CPUs become online, they are still mapped to
> hctx 0, then hctx 0 may become the bottleneck of IO dispatch and
> completion.
> 
> This patch sets up the mapping from the beginning, and aligns to
> queue mapping for PCI device (blk_mq_pci_map_queues()).

Please kill the now pointless cpu_to_queue_index function.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 2/8] blk-mq: don't keep offline CPUs mapped to hctx 0

[Sagi Grimberg]

Looks good,

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>