From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladislav Bolkhovitin Subject: Re: SRP Q's: 1) When is asynchronous I/O complete, 2) Is sequential I/O coalesced, and 3) why is iSCSI faster than SRP in some instances Date: Mon, 11 Jan 2010 21:44:01 +0300 Message-ID: <4B4B7171.4020000@vlnb.net> References: <1262829441.29991.10.camel@obelisk.thedillows.org> <1262989053.14204.21.camel@obelisk.thedillows.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Chris Worley Cc: David Dillow , OFED mailing list , scst-devel List-Id: linux-rdma@vger.kernel.org Chris Worley, on 01/09/2010 01:39 AM wrote: >>> I thought if the device was opened with the O_DIRECT flag, then the >>> scheduler should have nothing to coalesce. >> Depends on how many I/Os your application has in flight at once, >> assuming it is using AIO or threads. If you have more requests in flight >> than can be queued, the block layer will coalesce if possible. > > I do use AIO, always 64 threads, each w/ 64 outstanding I/O's. Local > or iSER initiator based, I never see any coalescing. Only w/ SRP. SRP initiator seems to be not too well optimized for the best performance. ISER initiator is noticeably better in this area. > There is the scst_vdisk "Direct I/O" option that's been commented out > of the code, as it's not supposed to work... maybe direct I/O doesn't > work... but that would be the target side. O_DIRECT for vdisk is supposed to work. It's a matter of a small patch for the kernel, see http://scst.sourceforge.net/contributing.html#O_DIRECT. Meanwhile, you can use fileio_tgt handler, with which O_DIRECT works well. Vlad -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html