From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1424520AbcBQXIR (ORCPT ); Wed, 17 Feb 2016 18:08:17 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:18664 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1424503AbcBQXIP (ORCPT ); Wed, 17 Feb 2016 18:08:15 -0500 To: Jan Kara Cc: Changho Choi-SSI , "lsf-pc\@lists.linux-foundation.org" , linux-fsdevel@vger.kernel.org, LKML Subject: Re: [Lsf-pc] [LSF/MM TOPIC] multi-stream IO hint implementation proposal for LSF/MM 2016 From: "Martin K. Petersen" Organization: Oracle Corporation References: <8F1CD504A027484E89249BCD2A7248DD573D15D9@SSIEXCH-MB3.ssi.samsung.com> <20160217152155.GA14140@quack.suse.cz> Date: Wed, 17 Feb 2016 18:08:04 -0500 In-Reply-To: <20160217152155.GA14140@quack.suse.cz> (Jan Kara's message of "Wed, 17 Feb 2016 16:21:55 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>>>> "Jan" == Jan Kara writes: Jan> So a key question for a feature like this is: How many stream IDs Jan> are devices going to support? Because AFAIR so far the answer was Jan> "it depends on the device". However the design how stream IDs can Jan> be used greatly differs between "a couple of stream IDs" and Jan> e.g. 2^32 stream IDs. Without this information I don't think the Jan> discussion would be very useful. So can you provide some rough Jan> numbers? Both SCSI and NVMe have a 16-bit stream ID field. So you are capped at 64K unique identifiers. However, the number of streams a device can have open concurrently is expected to be much smaller than that. This leaves us with the interesting problem of how to divide up the available streams. Whether to support application- and kernel allocated streams concurrently. And how we deal with explicitly closing streams after use. -- Martin K. Petersen Oracle Linux Engineering