From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladislav Bolkhovitin Subject: Re: Performance of SCST versus STGT Date: Tue, 22 Jan 2008 15:20:44 +0300 Message-ID: <4795DF9C.4000809@vlnb.net> References: <20080122122657R.fujita.tomonori@lab.ntt.co.jp> <4795D479.1080805@vlnb.net> <20080122204845E.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-relay-01.mailcluster.net ([77.221.130.213]:55168 "EHLO mail-relay-01.mailcluster.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751947AbYAVMUi (ORCPT ); Tue, 22 Jan 2008 07:20:38 -0500 In-Reply-To: <20080122204845E.fujita.tomonori@lab.ntt.co.jp> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: FUJITA Tomonori Cc: bart.vanassche@gmail.com, stgt-devel@lists.berlios.de, linux-scsi@vger.kernel.org, scst-devel@lists.sourceforge.net, pw@osc.edu, James.Bottomley@hansenpartnership.com, erezz@voltaire.com FUJITA Tomonori wrote: > On Tue, 22 Jan 2008 14:33:13 +0300 > Vladislav Bolkhovitin wrote: > > >>FUJITA Tomonori wrote: >> >>>The big problem of stgt iSER is disk I/Os (move data between disk and >>>page cache). We need a proper asynchronous I/O mechanism, however, >>>Linux doesn't provide such and we use a workaround, which incurs large >>>latency. I guess, we cannot solve this until syslets is merged into >>>mainline. >> >>Hmm, SCST also doesn't have ability to use asynchronous I/O, but that >>doesn't prevent it from showing good performance. > > > I don't know how SCST performs I/Os, but surely, in kernel space, you > can performs I/Os asynchronously. Sure, but currently it all synchronous > Or you use an event notification > mechanism with multiple kernel threads performing I/Os synchronously. > > Xen blktap has the same problem as stgt. IIRC, Xen mainline uses a > kernel patch to add a proper event notification to AIO though redhat > uses the same workaround as stgt instead of applying the kernel patch. > - > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >