[Bionic][PATCH v3 12/21] blk-mq: don't keep offline CPUs mapped to hctx 0

Jose Ricardo Ziviani joserz at linux.vnet.ibm.com
Tue May 15 13:03:15 UTC 2018

From: Ming Lei <ming.lei at redhat.com>

BugLink: http://bugs.launchpad.net/bugs/1759723

>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

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 at linux.vnet.ibm.com>
Cc: Keith Busch <keith.busch at intel.com>
Cc: stable at vger.kernel.org
Fixes: 4b855ad37194 ("blk-mq: Create hctx for each present CPU)
Tested-by: Christian Borntraeger <borntraeger at de.ibm.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
Signed-off-by: Ming Lei <ming.lei at redhat.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
(cherry picked from commit bffa9909a6b48d8ca3398dec601bc9162a4020c4)
Signed-off-by: Jose Ricardo Ziviani <joserz at linux.ibm.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;

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