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Mon, 14 Dec 2020 09:36:31 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2F07D4C050; Mon, 14 Dec 2020 09:36:31 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 793874C046; Mon, 14 Dec 2020 09:36:29 +0000 (GMT) Received: from pomme.local (unknown [9.145.29.158]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 14 Dec 2020 09:36:29 +0000 (GMT) Subject: Re: [PATCH v12 00/31] Speculative page faults To: Joel Fernandes , Chinwen Chang Cc: Haiyan Song , akpm@linux-foundation.org, mhocko@kernel.org, peterz@infradead.org, kirill@shutemov.name, ak@linux.intel.com, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , aneesh.kumar@linux.ibm.com, benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , sergey.senozhatsky.work@gmail.com, Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, Daniel Jordan , David Rientjes , Jerome Glisse , Ganesh Mahendran , Minchan Kim , Punit Agrawal , vinayak menon , Yang Shi , zhong jiang , Balbir Singh , sj38.park@gmail.com, Michel Lespinasse , Mike Rapoport , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, npiggin@gmail.com, paulmck@linux.vnet.ibm.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org, miles.chen@mediatek.com References: <20190416134522.17540-1-ldufour@linux.ibm.com> <20190606065129.d5s3534p23twksgp@haiyan.sh.intel.com> <3d3cefa2-0ebb-e86d-b060-7ba67c48a59f@linux.ibm.com> <1c412ebe-c213-ee67-d261-c70ddcd34b79@linux.ibm.com> <20190620081945.hwj6ruqddefnxg6z@haiyan.sh.intel.com> <1594027500.30360.32.camel@mtkswgap22> <490c0811-50cd-0802-2cbc-9c031ef309f6@linux.ibm.com> <1594099897.30360.58.camel@mtkswgap22> From: Laurent Dufour Message-ID: Date: Mon, 14 Dec 2020 10:36:29 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2020-12-14_04:2020-12-11,2020-12-14 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 bulkscore=0 clxscore=1011 malwarescore=0 suspectscore=0 adultscore=0 mlxlogscore=999 impostorscore=0 mlxscore=0 lowpriorityscore=0 priorityscore=1501 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012140067 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Le 14/12/2020 =C3=A0 03:03, Joel Fernandes a =C3=A9crit=C2=A0: > On Tue, Jul 07, 2020 at 01:31:37PM +0800, Chinwen Chang wrote: > [..] >>>> Hi Laurent, >>>> >>>> We merged SPF v11 and some patches from v12 into our platforms. Afte= r >>>> several experiments, we observed SPF has obvious improvements on the >>>> launch time of applications, especially for those high-TLP ones, >>>> >>>> # launch time of applications(s): >>>> >>>> package version w/ SPF w/o SPF improve(%) >>>> ------------------------------------------------------------------ >>>> Baidu maps 10.13.3 0.887 0.98 9.49 >>>> Taobao 8.4.0.35 1.227 1.293 5.10 >>>> Meituan 9.12.401 1.107 1.543 28.26 >>>> WeChat 7.0.3 2.353 2.68 12.20 >>>> Honor of Kings 1.43.1.6 6.63 6.713 1.24 >>> >>> That's great news, thanks for reporting this! >>> >>>> >>>> By the way, we have verified our platforms with those patches and >>>> achieved the goal of mass production. >>> >>> Another good news! >>> For my information, what is your targeted hardware? >>> >>> Cheers, >>> Laurent. >> >> Hi Laurent, >> >> Our targeted hardware belongs to ARM64 multi-core series. >=20 > Hello! >=20 > I was trying to develop an intuition about why does SPF give improvemen= t for > you on small CPU systems. This is just a high-level theory but: >=20 > 1. Assume the improvement is because of elimination of "blocking" on > mmap_sem. > Could it be that the mmap_sem is acquired in write-mode unnecessarily i= n some > places, thus causing blocking on mmap_sem in other paths? If so, is it > feasible to convert such usages to acquiring them in read-mode? That's correct, and the goal of this series is to try not holding the mma= p_sem=20 in read mode during page fault processing. Converting mmap_sem holder from write to read mode is not so easy and tha= t work=20 as already been done in some places. If you think there are areas where t= his=20 could be done, you're welcome to send patches fixing that. > 2. Assume the improvement is because of lesser read-side contention on > mmap_sem. > On small CPU systems, I would not expect reducing cache-line bouncing t= o give > such a dramatic improvement in performance as you are seeing. I don't think cache line bouncing reduction is the main sourcec of perfor= mance=20 improvement, I would rather think this is the lower part here. I guess this is mainly because during loading time a lot of page fault is= =20 occuring and thus SPF is reducing the contention on the mmap_sem. > Thanks for any insight on this! >=20 > - Joel >=20