Messages in this thread Patch in this message | | | Date | Wed, 08 Oct 2014 15:16:37 +0200 | From | Bart Van Assche <> | Subject | [PATCH] blk-mq: Use all available hardware queues |
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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: Christoph Hellwig <hch@lst.de> Cc: Ming Lei <ming.lei@canonical.com> --- block/blk-mq-cpumap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c index 1065d7c..8e56455 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) -- 1.8.4.5
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