blk-mq: don't keep offline CPUs mapped to hctx 0

Ming Lei · axboe · commit bffa9909a6b4 · 2018-04-10T08:38:46.000-06:00
From commit 4b855ad ("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()). Cc: Stefan Haberland <sth@linux.vnet.ibm.com> Cc: Keith Busch <keith.busch@intel.com> Cc: stable@vger.kernel.org Fixes: 4b855ad ("blk-mq: Create hctx for each present CPU) Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Sagi Grimberg <sagi@grimberg.me> Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git 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;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -16,11 +16,6 @@`
`16`	`16`
`17`	`17`	`static int cpu_to_queue_index(unsigned int nr_queues, const int cpu)`
`18`	`18`	`{`
`19`		`- /*`
`20`		`- * Non present CPU will be mapped to queue index 0.`
`21`		`- */`
`22`		`- if (!cpu_present(cpu))`
`23`		`- return 0;`
`24`	`19`	`return cpu % nr_queues;`
`25`	`20`	`}`
`26`	`21`