From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752680AbbCXWHX (ORCPT ); Tue, 24 Mar 2015 18:07:23 -0400 Received: from mx2.ssi.samsung.com ([207.140.43.206]:34632 "EHLO mx2.ssi.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752117AbbCXWHT convert rfc822-to-8bit (ORCPT ); Tue, 24 Mar 2015 18:07:19 -0400 X-ASG-Debug-ID: 1427234838-03754d34d631780001-xx1T2L X-Barracuda-Envelope-From: ming.l@ssi.samsung.com X-Barracuda-Apparent-Source-IP: 105.128.134.172 X-ASG-Whitelist: Client From: Ming Lin-SSI To: Jens Axboe , =?iso-8859-1?Q?Matias_Bj=F8rling?= , Jens Axboe , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" Subject: RE: [PATCH 1/6] block: add support for carrying a stream ID in a bio Thread-Topic: [PATCH 1/6] block: add support for carrying a stream ID in a bio X-ASG-Orig-Subj: RE: [PATCH 1/6] block: add support for carrying a stream ID in a bio Thread-Index: AQHQZkb+Rx1dSF4ahUOL5qRm6WpMrZ0sU9YAgAAEZgD//9iJoA== Date: Tue, 24 Mar 2015 22:07:11 +0000 Message-ID: <3A47B4705F6BE24CBB43C61AA73286215067DA@SSIEXCH-MB3.ssi.samsung.com> References: <1427210823-5283-1-git-send-email-axboe@fb.com> <1427210823-5283-2-git-send-email-axboe@fb.com> <55119AAE.9030202@bjorling.me> <55119E5E.6020405@kernel.dk> In-Reply-To: <55119E5E.6020405@kernel.dk> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [105.128.12.106] Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-CFilter-Loop: Reflected X-Barracuda-Connect: UNKNOWN[105.128.134.172] X-Barracuda-Start-Time: 1427234838 X-Barracuda-URL: http://mx1.ssi.samsung.com:8000/cgi-mod/mark.cgi X-Barracuda-BRTS-Status: 1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Jens Axboe [mailto:axboe@kernel.dk] > Sent: Tuesday, March 24, 2015 10:27 AM > To: Matias Bjørling; Jens Axboe; linux-kernel@vger.kernel.org; linux- > fsdevel@vger.kernel.org > Cc: Ming Lin-SSI > Subject: Re: [PATCH 1/6] block: add support for carrying a stream ID in a bio > > On 03/24/2015 11:11 AM, Matias Bjørling wrote: > > On 03/24/2015 04:26 PM, Jens Axboe wrote: > >> The top bits of bio->bi_flags are reserved for keeping the allocation > >> pool, set aside the next four bits for carrying a stream ID. That > >> leaves us with support for 15 streams, > >> 0 is reserved as a "stream not set" value. > > > > 15 streams seem very limited. Can this be extended? e.g. 16 bits. > > > > 15 streams is enough for 1-4 applications. More, and applications > > starts to fight over the same stream id's, leading them to place > > different age data in same flash blocks and push us back to square one. > > > > I understand that Samsung multi-stream SSD supports a limited amount > > of streams, more advance implementations should provide higher limits. > > Pushing it higher is not a big deal as far as the implementation goes, though > 16 bits might be stealing a bit too much space for this. On 32-bit archs, we > have 18 bits currently free that we can abuse. The Samsung device supports > 16 streams. That's honestly a lot more than I would expect most devices to > support in hardware, 16 is a lot of open erase blocks and write append points. > Obviously the open channel effort would make that more feasible, though. Can we use 8 bits at least? I'll test performance with 16 streams. > > -- > Jens Axboe