From: Ming Lei <ming.lei@redhat.com>
Date: Sun, 8 Apr 2018 09:48:08 +0000 (+0800)
Subject: blk-mq: don't keep offline CPUs mapped to hctx 0
X-Git-Tag: v4.19~1200^2~23
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=bffa9909a6b48d8ca3398dec601bc9162a4020c4;p=platform%2Fkernel%2Flinux-rpi.git

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

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()).

Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: stable@vger.kernel.org
Fixes: 4b855ad37194 ("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
index 9f8cffc..3eb169f 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;
 }