Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932342AbbFQPJP (ORCPT ); Wed, 17 Jun 2015 11:09:15 -0400 Received: from mail-la0-f53.google.com ([209.85.215.53]:36705 "EHLO mail-la0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932296AbbFQPJM (ORCPT ); Wed, 17 Jun 2015 11:09:12 -0400 MIME-Version: 1.0 In-Reply-To: References: <20150611211354.10271.57950.stgit@dwillia2-desk3.amr.corp.intel.com> <20150611211947.10271.80768.stgit@dwillia2-desk3.amr.corp.intel.com> <20150617113121.GC9246@lst.de> From: Andy Lutomirski Date: Wed, 17 Jun 2015 08:08:49 -0700 Message-ID: Subject: Re: [PATCH v4 6/6] arch, x86: pmem api for ensuring durability of persistent memory updates To: Dan Williams Cc: Christoph Hellwig , Arnd Bergmann , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Thomas Gleixner , Ross Zwisler , Andrew Morton , Juergen Gross , X86 ML , "Kani, Toshimitsu" , "linux-nvdimm@lists.01.org" , Benjamin Herrenschmidt , Luis Rodriguez , Konrad Rzeszutek Wilk , "linux-kernel@vger.kernel.org" , Stefan Bader , "linux-mm@kvack.org" , Geert Uytterhoeven , Ralf Baechle , Henrique de Moraes Holschuh , Michael Ellerman , Tejun Heo , Paul Mackerras Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1340 Lines: 34 On Wed, Jun 17, 2015 at 7:54 AM, Dan Williams wrote: > On Wed, Jun 17, 2015 at 4:31 AM, Christoph Hellwig wrote: >> This mess with arch_ methods and an ops vecor is almost unreadable. >> >> What's the problem with having something like: >> >> pmem_foo() >> { >> if (arch_has_pmem) // or sync_pmem >> arch_pmem_foo(); >> generic_pmem_foo(); >> } >> >> This adds a branch at runtime, but that shoudn't really be any slower >> than an indirect call on architectures that matter. > > No doubt it's premature optimization, but it bothered me that we'll > end up calling cpuid perhaps multiple times every i/o. If it's just a > readability concern I could wrap it in helpers. Getting it upstream > is my primary concern at this point so I have no strong attachment to > the indirect calls if that's all that is preventing an ack. A cpuid per i/o would be a killer, but the cpufeature code is way smarter than that. You want static_cpu_has, though -- it's even faster, since it gets patched at boot time. --Andy -- 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/