From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 1F6FF6B0006 for ; Wed, 28 Mar 2018 20:18:00 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id v25so2369709pgn.20 for ; Wed, 28 Mar 2018 17:18:00 -0700 (PDT) Received: from mga11.intel.com (mga11.intel.com. [192.55.52.93]) by mx.google.com with ESMTPS id x4-v6si4550273plw.354.2018.03.28.17.17.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 28 Mar 2018 17:17:58 -0700 (PDT) Subject: Re: [PATCH 00/11] Use global pages with PTI References: <20180323174447.55F35636@viggo.jf.intel.com> <20180327200719.lvdomez6hszpmo4s@gmail.com> From: Dave Hansen Message-ID: <0d6ea030-ec3b-d649-bad7-89ff54094e25@linux.intel.com> Date: Wed, 28 Mar 2018 17:17:56 -0700 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: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar , Thomas Gleixner 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 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