From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758791Ab2DJNhP (ORCPT ); Tue, 10 Apr 2012 09:37:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53799 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752229Ab2DJNhL (ORCPT ); Tue, 10 Apr 2012 09:37:11 -0400 Date: Tue, 10 Apr 2012 09:37:09 -0400 From: Vivek Goyal To: linux kernel mailing list , Jens Axboe Cc: Moyer Jeff Moyer Subject: [RFC PATCH] block: Change default IO scheduler to deadline except SATA Message-ID: <20120410133708.GE21801@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I am wondering if CFQ as default scheduler is still the right choice. CFQ generally works well on slow rotational media (SATA?). But often underperforms on faster storage (storage arrays, PCIE SSDs, virtualized disk in linux guests etc). People often put logic in user space to tune their systems and change IO scheduler to deadline to get better performance on faster storage. Though there is not one good answer for all kind of storage and for all kind of workloads, I am wondering if we can provide a better default and that is change default IO scheduler to "deadline" except SATA. One can argue that some SAS disks can be slow too and benefit from CFQ. Yes, but default IO scheduler choice is not perfect anyway. It just tries to cater to a wide variety of use cases out of the box. So I am throwing this patch out see if it flies. Personally, I think it might turn out to be a more reasonable default. Thanks Vivek Change default IO scheduler to deadline except SATA disks. Signed-off-by: Vivek Goyal --- block/Kconfig.iosched | 2 +- block/elevator.c | 2 +- drivers/ata/libata-scsi.c | 4 ++++ include/linux/elevator.h | 2 ++ 4 files changed, 8 insertions(+), 2 deletions(-) Index: linux-2.6/block/Kconfig.iosched =================================================================== --- linux-2.6.orig/block/Kconfig.iosched 2012-04-09 22:18:30.941885325 -0400 +++ linux-2.6/block/Kconfig.iosched 2012-04-09 22:18:51.982885971 -0400 @@ -45,7 +45,7 @@ config CFQ_GROUP_IOSCHED choice prompt "Default I/O scheduler" - default DEFAULT_CFQ + default DEFAULT_DEADLINE help Select the I/O scheduler which will be used by default for all block devices. Index: linux-2.6/drivers/ata/libata-scsi.c =================================================================== --- linux-2.6.orig/drivers/ata/libata-scsi.c 2012-04-09 22:18:30.946885325 -0400 +++ linux-2.6/drivers/ata/libata-scsi.c 2012-04-10 01:09:10.529292695 -0400 @@ -1146,6 +1146,10 @@ static int ata_scsi_dev_config(struct sc blk_queue_flush_queueable(q, false); + /* Change IO scheduler to CFQ */ + if (!(*chosen_elevator)) + elevator_change(q, "cfq"); + dev->sdev = sdev; return 0; } Index: linux-2.6/block/elevator.c =================================================================== --- linux-2.6.orig/block/elevator.c 2012-04-09 22:18:30.000000000 -0400 +++ linux-2.6/block/elevator.c 2012-04-10 20:11:10.296866631 -0400 @@ -130,7 +130,7 @@ static int elevator_init_queue(struct re return -ENOMEM; } -static char chosen_elevator[ELV_NAME_MAX]; +char chosen_elevator[ELV_NAME_MAX]; static int __init elevator_setup(char *str) { Index: linux-2.6/include/linux/elevator.h =================================================================== --- linux-2.6.orig/include/linux/elevator.h 2012-03-13 01:07:29.000000000 -0400 +++ linux-2.6/include/linux/elevator.h 2012-04-10 01:07:44.303289797 -0400 @@ -204,5 +204,7 @@ enum { INIT_LIST_HEAD(&(rq)->csd.list); \ } while (0) +extern char chosen_elevator[]; + #endif /* CONFIG_BLOCK */ #endif