linux-kernel - [PATCH] blk-mq: Use all available hardware queues

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <54353935.5010300@acm.org>
Date:	Wed, 08 Oct 2014 15:16:37 +0200
From:	Bart Van Assche <bvanassche@....org>
To:	Jens Axboe <axboe@...nel.dk>
CC:	Christoph Hellwig <hch@...radead.org>,
	Sagi Grimberg <sagig@...lanox.com>,
	Sebastian Parschauer <sebastian.riemer@...fitbricks.com>,
	Robert Elliott <Elliott@...com>,
	Ming Lei <ming.lei@...onical.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] 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@....org>
Reviewed-by: Sagi Grimberg <sagig@...lanox.com>
Cc: Christoph Hellwig <hch@....de>
Cc: Ming Lei <ming.lei@...onical.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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/