From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F121AC433E2 for ; Sun, 30 Aug 2020 10:14:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9DE1207DA for ; Sun, 30 Aug 2020 10:14:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726984AbgH3KOj (ORCPT ); Sun, 30 Aug 2020 06:14:39 -0400 Received: from out30-57.freemail.mail.aliyun.com ([115.124.30.57]:39051 "EHLO out30-57.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726264AbgH3KOi (ORCPT ); Sun, 30 Aug 2020 06:14:38 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04392;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=8;SR=0;TI=SMTPD_---0U7FapVA_1598782473; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0U7FapVA_1598782473) by smtp.aliyun-inc.com(127.0.0.1); Sun, 30 Aug 2020 18:14:34 +0800 Subject: Re: [PATCH v2 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags To: Anshuman Khandual , Matthew Wilcox , David Hildenbrand Cc: Andrew Morton , Hugh Dickins , Alexander Duyck , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1597816075-61091-1-git-send-email-alex.shi@linux.alibaba.com> <8ec2a4b0-9e51-abf9-fa7a-29989d3f1fac@arm.com> From: Alex Shi Message-ID: <01c846d4-2fe4-eeef-6c79-e71fda1f9a39@linux.alibaba.com> Date: Sun, 30 Aug 2020 18:14:33 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <8ec2a4b0-9e51-abf9-fa7a-29989d3f1fac@arm.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2020/8/19 下午3:55, Anshuman Khandual 写道: > > > On 08/19/2020 11:17 AM, Alex Shi wrote: >> pageblock_flags is used as long, since every pageblock_flags is just 4 >> bits, 'long' size will include 8(32bit machine) or 16 pageblocks' flags, >> that flag setting has to sync in cmpxchg with 7 or 15 other pageblock >> flags. It would cause long waiting for sync. >> >> If we could change the pageblock_flags variable as char, we could use >> char size cmpxchg, which just sync up with 2 pageblock flags. it could >> relief much false sharing in cmpxchg. > > Do you have numbers demonstrating claimed performance improvement > after this change ? > the performance data show in another email. LKP reported the arm6 has a bug on this patchset, since it has no cmpxchgb solution, so maybe let's fallback to cmpxchg on it. >From db3d97ba8cc5e206b440bd40a92ef6955ad86bc0 Mon Sep 17 00:00:00 2001 From: Alex Shi Date: Tue, 18 Aug 2020 15:51:18 +0800 Subject: [PATCH v2 3/3] armv6: fix armv6 build issue Arm v6 can not simulate cmpxchg1 func, so we have to use cmpxchg4 on it. arm-linux-gnueabi-ld: mm/page_alloc.o: in function `set_pfnblock_flags_mask': (.text+0x32b4): undefined reference to `__bad_cmpxchg' arm-linux-gnueabi-ld: (.text+0x32e0): undefined reference to `__bad_cmpxchg' arm-linux-gnueabi-ld: drivers/net/ethernet/aquantia/atlantic/hw_atl/hw_atl_b0.o: in function `hw_atl_b0_get_mac_temp': hw_atl_b0.c:(.text+0x30fc): undefined reference to `__bad_udelay' Reported-by: kernel test robot Signed-off-by: Alex Shi Cc: Andrew Morton Cc: Baolin Wang Cc: Russell King Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org --- mm/page_alloc.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7da09d66233b..c09146a8946c 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -517,7 +517,11 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, { unsigned char *bitmap; unsigned long bitidx, byte_bitidx; +#ifdef CONFIG_CPU_V6 + unsigned long old_byte, byte; +#else unsigned char old_byte, byte; +#endif BUILD_BUG_ON(NR_PAGEBLOCK_BITS != BITS_PER_BYTE); BUILD_BUG_ON(MIGRATE_TYPES > (1 << PB_migratetype_bits)); @@ -532,9 +536,18 @@ void set_pfnblock_flags_mask(struct page *page, unsigned long flags, mask <<= bitidx; flags <<= bitidx; +#ifdef CONFIG_CPU_V6 + byte = (unsigned long)READ_ONCE(bitmap[byte_bitidx]); +#else byte = READ_ONCE(bitmap[byte_bitidx]); +#endif for (;;) { +#ifdef CONFIG_CPU_V6 + /* arm v6 has no cmpxchgb function, so still false sharing long word */ + old_byte = cmpxchg((unsigned long*)&bitmap[byte_bitidx], byte, (byte & ~mask) | flags); +#else old_byte = cmpxchg(&bitmap[byte_bitidx], byte, (byte & ~mask) | flags); +#endif if (byte == old_byte) break; byte = old_byte; -- 1.8.3.1