From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751043AbeC2ASA (ORCPT ); Wed, 28 Mar 2018 20:18:00 -0400 Received: from mga03.intel.com ([134.134.136.65]:13538 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750733AbeC2AR6 (ORCPT ); Wed, 28 Mar 2018 20:17:58 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.48,374,1517904000"; d="scan'208";a="212171952" Subject: Re: [PATCH 00/11] Use global pages with PTI To: Ingo Molnar , Thomas Gleixner References: <20180323174447.55F35636@viggo.jf.intel.com> <20180327200719.lvdomez6hszpmo4s@gmail.com> Cc: Linus Torvalds , Linux Kernel Mailing List , linux-mm , Andrea Arcangeli , Andrew Lutomirski , Kees Cook , Hugh Dickins , =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , the arch/x86 maintainers , namit@vmware.com From: Dave Hansen Message-ID: <0d6ea030-ec3b-d649-bad7-89ff54094e25@linux.intel.com> Date: Wed, 28 Mar 2018 17:17:56 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180327200719.lvdomez6hszpmo4s@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/27/2018 01:07 PM, Ingo Molnar wrote: > * Thomas Gleixner wrote: >>> systems. Atoms are going to be the easiest thing to get my hands on, >>> but I tend to shy away from them for performance work. >> What I have in mind is that I wonder whether the whole circus is worth it >> when there is no performance advantage on PCID systems. I was waiting on trying to find a relatively recent Atom system (they actually come in reasonably sized servers [1]), but I'm hitting a snag there, so I figured I'd just share a kernel compile using Ingo's perf-based methodology on a Skylake desktop system with PCIDs. Here's the kernel compile: No Global pages (baseline): 186.951 seconds time elapsed ( +- 0.35% ) 28 Global pages (this set): 185.756 seconds time elapsed ( +- 0.09% ) -1.195 seconds (-0.64%) Lower is better here, obviously. I also re-checked everything using will-it-scale's llseek1 test[2] which is basically a microbenchmark of a halfway reasonable syscall. Higher here is better. No Global pages (baseline): 15783951 lseeks/sec 28 Global pages (this set): 16054688 lseeks/sec +270737 lseeks/sec (+1.71%) So, both the kernel compile and the microbenchmark got measurably faster. 1. https://ark.intel.com/products/97933/Intel-Atom-Processor-C3955-16M-Cache-up-to-2_40-GHz 2. https://github.com/antonblanchard/will-it-scale/blob/master/tests/lseek1.c