Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752770AbaKGRlL (ORCPT ); Fri, 7 Nov 2014 12:41:11 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:49095 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752127AbaKGRlJ (ORCPT ); Fri, 7 Nov 2014 12:41:09 -0500 To: "Elliott\, Robert \(Server Storage\)" Cc: "Martin K. Petersen" , Chris Friesen , Jens Axboe , lkml , "linux-scsi\@vger.kernel.org" , Mike Snitzer Subject: Re: absurdly high "optimal_io_size" on Seagate SAS disk From: "Martin K. Petersen" Organization: Oracle Corporation References: <545BA625.40308@windriver.com> <545BAD05.3050800@windriver.com> <545BB3AB.8070409@windriver.com> <545BC88A.7060706@windriver.com> <94D0CD8314A33A4D9D801C0FE68B40295937AE5D@G4W3202.americas.hpqcorp.net> Date: Fri, 07 Nov 2014 12:40:59 -0500 In-Reply-To: <94D0CD8314A33A4D9D801C0FE68B40295937AE5D@G4W3202.americas.hpqcorp.net> (Robert Elliott's message of "Fri, 7 Nov 2014 17:10:34 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Source-IP: acsinet21.oracle.com [141.146.126.237] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>>>> "Rob" == Elliott, Robert (Server Storage) writes: Rob, Rob> * the block layer BIO_MAX_PAGES value of 256 limits IOs Rob> to a maximum of 1 MiB We do support scatterlist chaining, though. Rob> * SCSI LLDs report their maximum transfer size in Rob> /sys/block/sdNN/queue/max_hw_sectors_kb Rob> * the SCSI midlayer maximum transfer size is set/reported Rob> in /sys/block/sdNN/queue/max_sectors_kb and the default is 512 Rob> KiB Rob> * the SCSI LLD maximum number of scatter gather entries Rob> reported in /sys/block/sdNN/queue/max_segments and Rob> /sys/block/sdNN/queue/max_segment_size creates a limit based on Rob> how fragmented the data buffer is in virtual memory Rob> * the Block Limits VPD page MAXIMUM TRANSFER LENGTH field Rob> indicates the maximum transfer size for one command over the SCSI Rob> transport protocol supported by the drive itself Yep. We're already capping the actual max I/O size based on all of the above. However, the purpose of exposing io_opt was to be able to report stripe size to partitioning tools and filesystems for alignment purposes. And although they would ideally be the same it was always anticipated that stripe size could be bigger than the max I/O size. -- Martin K. Petersen Oracle Linux Engineering -- 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/