linux-kernel - [PATCH] block/mq: blk map queues by core id

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Date:   Fri, 22 Mar 2019 18:09:49 +0800
From:   luferry <luferry@....com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Ming Lei <ming.lei@...hat.com>, Christoph Hellwig <hch@....de>,
        xuyun <luferry@....com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] block/mq: blk map queues by core id

under virtual machine environment, cpu topology may differ from normal
physical server.
for example (machine with 4 cores, 2 threads per core):

normal physical server:
core-id   thread-0-id  thread-1-id
0         0            4
1         1            5
2         2            6
3         3            7

virtual machine:
core-id   thread-0-id  thread-1-id
0         0            1
1         2            3
2         4            5
3         6            7

When attach disk with two queues, all the even numbered cpus will be
mapped to queue 0. Under virtual machine, all the cpus is followed by
its sibling cpu.Before this patch, all the odd numbered cpus will also
be mapped to queue 0, can cause serious imbalance.this will lead to
performance impact on system IO

So suggest to allocate cpu map by core id, this can be more currency

Signed-off-by: luferry <luferry@....com>
---
 block/blk-mq-cpumap.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 03a534820271..4125e8e77679 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -35,7 +35,7 @@ int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
 {
 	unsigned int *map = qmap->mq_map;
 	unsigned int nr_queues = qmap->nr_queues;
-	unsigned int cpu, first_sibling;
+	unsigned int cpu, first_sibling, core = 0;
 
 	for_each_possible_cpu(cpu) {
 		/*
@@ -48,9 +48,10 @@ int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
 			map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);
 		} else {
 			first_sibling = get_first_sibling(cpu);
-			if (first_sibling == cpu)
-				map[cpu] = cpu_to_queue_index(qmap, nr_queues, cpu);
-			else
+			if (first_sibling == cpu) {
+				map[cpu] = cpu_to_queue_index(qmap, nr_queues, core);
+				core++;
+			} else
 				map[cpu] = map[first_sibling];
 		}
 	}
-- 
2.14.1.40.g8e62ba1