From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751148AbdJCIDu (ORCPT ); Tue, 3 Oct 2017 04:03:50 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:43604 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751059AbdJCIDr (ORCPT ); Tue, 3 Oct 2017 04:03:47 -0400 Subject: Re: [PATCH v3 00/20] Speculative page faults To: Michael Ellerman , Andrew Morton Cc: Alexei Starovoitov , Paul McKenney , Peter Zijlstra , kirill@shutemov.name, Andi Kleen , Michal Hocko , dave@stgolabs.net, Jan Kara , Matthew Wilcox , Benjamin Herrenschmidt , Paul Mackerras , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Will Deacon , Sergey Senozhatsky , "linux-kernel@vger.kernel.org" , linux-mm , haren@linux.vnet.ibm.com, Anshuman Khandual , npiggin@gmail.com, bsingharora@gmail.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, "x86@kernel.org" References: <20170925163443.260d6092160ec704e2b04653@linux-foundation.org> <924a79af-6d7a-316a-1eee-3aebbfd4addf@linux.vnet.ibm.com> <20170928133850.90c5bf2aac0f1a63e29c01a3@linux-foundation.org> <64e9759b-a4fb-63d3-a811-3e35ae5a1028@linux.vnet.ibm.com> <873771dnrl.fsf@concordia.ellerman.id.au> From: Laurent Dufour Date: Tue, 3 Oct 2017 10:03:18 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <873771dnrl.fsf@concordia.ellerman.id.au> Content-Type: text/plain; charset=utf-8 Content-Language: fr Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 17100308-0012-0000-0000-0000057DFFAA X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17100308-0013-0000-0000-000018F7697C Message-Id: <177195b3-2d99-94e6-f334-843bd19042a1@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-03_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710030119 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/10/2017 03:27, Michael Ellerman wrote: > Laurent Dufour writes: > >> Hi Andrew, >> >> On 28/09/2017 22:38, Andrew Morton wrote: >>> On Thu, 28 Sep 2017 14:29:02 +0200 Laurent Dufour wrote: >>> >>>>> Laurent's [0/n] provides some nice-looking performance benefits for >>>>> workloads which are chosen to show performance benefits(!) but, alas, >>>>> no quantitative testing results for workloads which we may suspect will >>>>> be harmed by the changes(?). Even things as simple as impact upon >>>>> single-threaded pagefault-intensive workloads and its effect upon >>>>> CONFIG_SMP=n .text size? >>>> >>>> I forgot to mention in my previous email the impact on the .text section. >>>> >>>> Here are the metrics I got : >>>> >>>> .text size UP SMP Delta >>>> 4.13-mmotm 8444201 8964137 6.16% >>>> '' +spf 8452041 8971929 6.15% >>>> Delta 0.09% 0.09% >>>> >>>> No major impact as you could see. >>> >>> 8k text increase seems rather a lot actually. That's a lot more >>> userspace cacheclines that get evicted during a fault... >>> >>> Is the feature actually beneficial on uniprocessor? >> >> This is useless on uniprocessor, and I will disable it on x86 when !SMP >> by not defining __HAVE_ARCH_CALL_SPF. >> So the speculative page fault handler will not be built but the vm >> sequence counter and the SCRU stuff will still be there. I may also make >> it disabled through macro when __HAVE_ARCH_CALL_SPF is not defined, but >> this may obfuscated the code a bit... >> >> On ppc64, as this feature requires book3s, it can't be built without SMP >> support. > > Book3S doesn't force SMP, eg. PMAC is Book3S but can be built with SMP=n. > > It's true that POWERNV and PSERIES both force SMP, and those are the > platforms used on modern Book3S CPUs. Thanks Michael, I'll add a check on CONFIG_SMP on ppc too. Laurent.