Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759464AbYBEQ0Z (ORCPT ); Tue, 5 Feb 2008 11:26:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759351AbYBEQZt (ORCPT ); Tue, 5 Feb 2008 11:25:49 -0500 Received: from rn-out-0910.google.com ([64.233.170.189]:55502 "EHLO rn-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759346AbYBEQZr (ORCPT ); Tue, 5 Feb 2008 11:25:47 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=a5NlLN3339L8q+gaoo5hcMOC+ipDKWc8ZJIM8o7d4TbetQ2y7VYNyfg1jRDx6NsMfoKOloywpfyXyY1v/XJf018Bn1MhjByxbumRGQ+gppG3ZZ9a/k1yEb8rhzJaNcX5RXljVfADFNuHROUAvc0sTUyuiy+GgYB5w+XkcF+hesU= Message-ID: Date: Tue, 5 Feb 2008 17:25:44 +0100 From: "Bart Van Assche" To: "James Bottomley" , "FUJITA Tomonori" , "Vladislav Bolkhovitin" , "Vu Pham" Subject: Re: Integration of SCST in the mainstream Linux kernel Cc: "Linus Torvalds" , "Andrew Morton" , linux-scsi@vger.kernel.org, scst-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, "Nicholas A. Bellinger" In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1201639331.3069.58.camel@localhost.localdomain> <47A05CBD.5050803@vlnb.net> <47A7049A.9000105@vlnb.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2732 Lines: 54 Regarding the performance tests I promised to perform: although until now I only have been able to run two tests (STGT + iSER versus SCST + SRP), the results are interesting. I will run the remaining test cases during the next days. About the test setup: dd and xdd were used to transfer 2 GB of data between an initiator system and a target system via direct I/O over an SDR InfiniBand network (1GB/s). The block size varied between 512 bytes and 1 GB, but was always a power of two. Expected results: * The measurement results are consistent with the numbers I published earlier. * During data transfers all data is transferred in blocks between 4 KB and 32 KB in size (according to the SCST statistics). * For small and medium block sizes (<= 32 KB) transfer times can be modeled very well by the following formula: (transfer time) = (setup latency) + (bytes transferred)/(bandwidth). The correlation numbers are very close to one. * The latency and bandwidth parameters depend on the test tool (dd versus xdd), on the kind of test performed (reading versus writing), on the SCSI target and on the communication protocol. * When using RDMA (iSER or SRP), SCST has a lower latency and higher bandwidth than STGT (results from linear regression for block sizes <= 32 KB): Test Latency(us) Bandwidth (MB/s) Correlation STGT+iSER, read, dd 64 560 0.999995 STGT+iSER, read, xdd 65 556 0.999994 STGT+iSER, write, dd 53 394 0.999971 STGT+iSER, write, xdd 54 445 0.999959 SCST+SRP, read, dd 39 657 0.999983 SCST+SRP, read, xdd 41 668 0.999987 SCST+SRP, write, dd 52 449 0.999962 SCST+SRP, write, xdd 52 516 0.999977 Results that I did not expect: * A block transfer size of 1 MB is not enough to measure the maximal throughput. The maximal throughput is only reached at much higher block sizes (about 10 MB for SCST + SRP and about 100 MB for STGT + iSER). * There is one case where dd and xdd results are inconsistent: when reading via SCST + SRP and for block sizes of about 1 MB. * For block sizes > 64 KB the measurements differ from the model. This is probably because all initiator-target transfers happen in blocks of 32 KB or less. For the details and some graphs, see also http://software.qlayer.com/display/iSCSI/Measurements . Bart Van Assche. -- 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/