path: root/block/blk-mq-cpumap.c
diff options
authorBart Van Assche <bvanassche@acm.org>2014-12-09 16:59:21 +0100
committerJens Axboe <axboe@fb.com>2014-12-09 09:08:21 -0700
commit959f5f5b2fa7ac3bdd37c91076e560c06513f1e6 (patch)
treea8a58d0da07019e2c75a0e236502cdd81c646336 /block/blk-mq-cpumap.c
parent52f7eb945f2ba62b324bb9ae16d945326a961dcf (diff)
blk-mq: Use all available hardware queues
Suppose that a system has two CPU sockets, three cores per socket, that it does not support hyperthreading and that four hardware queues are provided by a block driver. With the current algorithm this will lead to the following assignment of CPU cores to hardware queues: HWQ 0: 0 1 HWQ 1: 2 3 HWQ 2: 4 5 HWQ 3: (none) This patch changes the queue assignment into: HWQ 0: 0 1 HWQ 1: 2 HWQ 2: 3 4 HWQ 3: 5 In other words, this patch has the following three effects: - All four hardware queues are used instead of only three. - CPU cores are spread more evenly over hardware queues. For the above example the range of the number of CPU cores associated with a single HWQ is reduced from [0..2] to [1..2]. - If the number of HWQ's is a multiple of the number of CPU sockets it is now guaranteed that all CPU cores associated with a single HWQ reside on the same CPU socket. Signed-off-by: Bart Van Assche <bvanassche@acm.org> Reviewed-by: Sagi Grimberg <sagig@mellanox.com> Cc: Jens Axboe <axboe@fb.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Ming Lei <ming.lei@canonical.com> Cc: Alexander Gordeev <agordeev@redhat.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-mq-cpumap.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 72e5ed691e37..5f13f4d0bcce 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -17,7 +17,7 @@
static int cpu_to_queue_index(unsigned int nr_cpus, unsigned int nr_queues,
const int cpu)
- return cpu / ((nr_cpus + nr_queues - 1) / nr_queues);
+ return cpu * nr_queues / nr_cpus;
static int get_first_sibling(unsigned int cpu)