From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932946AbdEFDRd (ORCPT ); Fri, 5 May 2017 23:17:33 -0400 Received: from g9t5009.houston.hpe.com ([15.241.48.73]:44330 "EHLO g9t5009.houston.hpe.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750949AbdEFDRY (ORCPT ); Fri, 5 May 2017 23:17:24 -0400 From: "Kani, Toshimitsu" To: Dan Williams CC: "linux-kernel@vger.kernel.org" , "linux-block@vger.kernel.org" , "jmoyer@redhat.com" , "tglx@linutronix.de" , "hch@lst.de" , "viro@zeniv.linux.org.uk" , "x86@kernel.org" , "mawilcox@microsoft.com" , "hpa@zytor.com" , "linux-nvdimm@lists.01.org" , "mingo@redhat.com" , "linux-fsdevel@vger.kernel.org" , "ross.zwisler@linux.intel.com" , "jack@suse.cz" Subject: RE: [PATCH v2] x86, uaccess: introduce copy_from_iter_wt for pmem / writethrough operations Thread-Topic: [PATCH v2] x86, uaccess: introduce copy_from_iter_wt for pmem / writethrough operations Thread-Index: AQHSwFf2pYpBQohMYEm6dbBc4FPj86HmPreAgAAdeoCAAAVzgIAAOwEAgAAOubA= Date: Sat, 6 May 2017 03:17:19 +0000 Message-ID: References: <20170427063054.soejyqocqqrihfdw@gmail.com> <149340820800.28724.16189291963486607562.stgit@dwillia2-desk3.amr.corp.intel.com> <1494016773.30303.69.camel@hpe.com> <1494024273.30303.71.camel@hpe.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: intel.com; dkim=none (message not signed) header.d=none;intel.com; dmarc=none action=none header.from=hpe.com; x-originating-ip: [174.51.38.138] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;AT5PR84MB0259;7:BobhGyku2xCN6g3E05MDeaTdWH88ZNiW4FkaVjpem5hEemx16zi//HlxUFHJ2trZUABIjpWv2YX95J10XejY9CMgLW9ozX0bH1tlR9yEQW+hXljQ2zfV3d9dadXQL8G2fiIyV85W+mPhY8oFg2hw5lgSz2jEt7GC7/awgscfruMLRyWT8gFu6yet2Bl9l60qjr19Pw8PuLMDMi+I6UCFoYOx/pDrqng9T5Ub1Nq7mH2xrrR/J6hsOX/1xC5+85NlNbxscjzxC1KcCNzuQwTyQOywo15HsF2ua+MnJHdCspC2MesoC+5mcm4XQf6FJ1eDYDCDI2RWwcXLaUvGyTX/5Q== x-ms-office365-filtering-correlation-id: d403b52e-3d93-411c-d902-08d4942e67f4 x-ms-office365-filtering-ht: Tenant x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001)(2017030254075)(48565401081)(201703131423075)(201703031133081)(201702281549075);SRVR:AT5PR84MB0259; x-microsoft-antispam-prvs: x-exchange-antispam-report-test: UriScan:(227479698468861); x-exchange-antispam-report-cfa-test: BCL:0;PCL:0;RULEID:(6040450)(601004)(2401047)(5005006)(8121501046)(3002001)(10201501046)(93006095)(93001095)(6055026)(6041248)(20161123562025)(20161123558100)(201703131423075)(201702281528075)(201703061421075)(201703061406153)(20161123564025)(20161123555025)(20161123560025)(6072148);SRVR:AT5PR84MB0259;BCL:0;PCL:0;RULEID:;SRVR:AT5PR84MB0259; x-forefront-prvs: 029976C540 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(6009001)(39410400002)(39860400002)(39400400002)(39850400002)(39450400003)(39840400002)(24454002)(377424004)(377454003)(2900100001)(9686003)(25786009)(7736002)(53936002)(54906002)(53546009)(33656002)(4326008)(50986999)(7696004)(76176999)(8936002)(6246003)(93886004)(3280700002)(38730400002)(54356999)(229853002)(81166006)(8666007)(86362001)(8676002)(110136004)(6116002)(3846002)(6506006)(6436002)(3660700001)(55016002)(2950100002)(189998001)(6916009)(5660300001)(5250100002)(66066001)(74316002)(478600001)(102836003)(305945005);DIR:OUT;SFP:1102;SCL:1;SRVR:AT5PR84MB0259;H:AT5PR84MB0260.NAMPRD84.PROD.OUTLOOK.COM;FPR:;SPF:None;MLV:sfv;LANG:en; spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 X-MS-Exchange-CrossTenant-originalarrivaltime: 06 May 2017 03:17:19.7687 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 105b2061-b669-4b31-92ac-24d304d195dc X-MS-Exchange-Transport-CrossTenantHeadersStamped: AT5PR84MB0259 X-OriginatorOrg: hpe.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id v463HdGM024517 > On Fri, May 5, 2017 at 3:44 PM, Kani, Toshimitsu > wrote: > > On Fri, 2017-05-05 at 15:25 -0700, Dan Williams wrote: > >> On Fri, May 5, 2017 at 1:39 PM, Kani, Toshimitsu > >> wrote: > > : > >> > > --- > >> > > Changes since the initial RFC: > >> > > * s/writethru/wt/ since we already have ioremap_wt(), > >> > > set_memory_wt(), etc. (Ingo) > >> > > >> > Sorry I should have said earlier, but I think the term "wt" is > >> > misleading. Non-temporal stores used in memcpy_wt() provide WC > >> > semantics, not WT semantics. > >> > >> The non-temporal stores do, but memcpy_wt() is using a combination of > >> non-temporal stores and explicit cache flushing. > >> > >> > How about using "nocache" as it's been > >> > used in __copy_user_nocache()? > >> > >> The difference in my mind is that the "_nocache" suffix indicates > >> opportunistic / optional cache pollution avoidance whereas "_wt" > >> strictly arranges for caches not to contain dirty data upon > >> completion of the routine. For example, non-temporal stores on older > >> x86 cpus could potentially leave dirty data in the cache, so > >> memcpy_wt on those cpus would need to use explicit cache flushing. > > > > I see. I agree that its behavior is different from the existing one > > with "_nocache". That said, I think "wt" or "write-through" generally > > means that writes allocate cachelines and keep them clean by writing to > > memory. So, subsequent reads to the destination will hit the > > cachelines. This is not the case with this interface. > > True... maybe _nocache_strict()? Or, leave it _wt() until someone > comes along and is surprised that the cache is not warm for reads > after memcpy_wt(), at which point we can ask "why not just use plain > memcpy then?", or set the page-attributes to WT. I prefer _nocache_strict(), if it's not too long, since it avoids any confusion. If other arches actually implement it with WT semantics, we might become the one to change it, instead of the caller. Thanks, -Toshi