Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753558Ab0L0LUA (ORCPT ); Mon, 27 Dec 2010 06:20:00 -0500 Received: from mtagate6.uk.ibm.com ([194.196.100.166]:56823 "EHLO mtagate6.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753043Ab0L0LT7 (ORCPT ); Mon, 27 Dec 2010 06:19:59 -0500 From: Mustafa Mesanovic Organization: IBM To: dm-devel@redhat.com, akpm@linux-foundation.org, snitzer@redhat.com, neilb@suse.de Subject: [RFC][PATCH] dm: improve read performance Date: Mon, 27 Dec 2010 12:19:55 +0100 User-Agent: KMail/1.13.2 (Linux/2.6.35-22-customkernel; KDE/4.4.2; i686; ; ) Cc: linux-kernel@vger.kernel.org, heiko.carstens@de.ibm.com, cotte@de.ibm.com, ehrhardt@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Message-Id: <201012271219.56476.mume@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1891 Lines: 48 From: Mustafa Mesanovic A short explanation in prior: in this case we have "stacked" dm devices. Two multipathed luns combined together to one striped logical volume. I/O throughput degradation happens at __bio_add_page when bio's get checked upon max_sectors. In this setup max_sectors is always set to 8 -> what is 4KiB. A standalone striped logical volume on luns which are not multipathed do not have the problem: the logical volume will take over the max_sectors from luns below. Same happens with luns which are multipathed -> the multipathed targets have the same max_sectors as the luns below. So "magic" happens only when target has no own merge_fn and below lying devices have a merge function -> we got then max_sectors=PAGE_SIZE >> 9. This patch prevents that max_sectors will be set to PAGE_SIZE >> 9. Instead it will use the minimum max_sectors value from below devices. Using the patch improves read I/O up to 3x. In this specific case from 600MiB/s up to 1800MiB/s. Signed-off-by: Mustafa Mesanovic --- dm-table.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: linux-2.6/drivers/md/dm-table.c =================================================================== --- linux-2.6.orig/drivers/md/dm-table.c 2010-12-23 13:49:18.000000000 +0100 +++ linux-2.6/drivers/md/dm-table.c 2010-12-23 13:50:22.000000000 +0100 @@ -518,7 +518,7 @@ if (q->merge_bvec_fn && !ti->type->merge) blk_limits_max_hw_sectors(limits, - (unsigned int) (PAGE_SIZE >> 9)); + q->limits.max_sectors); return 0; } EXPORT_SYMBOL_GPL(dm_set_device_limits); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/