From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: [PATCH RFC 0/8] IB/srp: Add multichannel support Date: Fri, 19 Sep 2014 14:56:23 +0200 Message-ID: <541C27F7.1020509@acm.org> References: <541C27BF.6070609@acm.org> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <541C27BF.6070609@acm.org> Sender: linux-scsi-owner@vger.kernel.org To: "linux-scsi@vger.kernel.org" Cc: linux-rdma , Christoph Hellwig , Jens Axboe , Robert Elliott , Ming Lei List-Id: linux-rdma@vger.kernel.org [PATCH 1/8] 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 Cc: Jens Axboe Cc: Christoph Hellwig Cc: Ming Lei --- 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