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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E74FC77B7A for ; Tue, 6 Jun 2023 21:26:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239706AbjFFV0H (ORCPT ); Tue, 6 Jun 2023 17:26:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42060 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238613AbjFFV0D (ORCPT ); Tue, 6 Jun 2023 17:26:03 -0400 Received: from mail-pg1-f180.google.com (mail-pg1-f180.google.com [209.85.215.180]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0D9761703 for ; Tue, 6 Jun 2023 14:26:03 -0700 (PDT) Received: by mail-pg1-f180.google.com with SMTP id 41be03b00d2f7-53404873a19so3459584a12.3 for ; Tue, 06 Jun 2023 14:26:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1686086762; x=1688678762; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=zC4QoBDS/PVcd+xuGELUqjLK2nruU3LnP3t1Jluqdlw=; b=is6Lqv6XZpAvGIxIG3JcNVC4C9OfiuXU27JTYhYoysYh3Kghs9hvkIF9FQVIBy9wu5 f4kV4dF1ML6/sFhv6bSbrobZQYO1MFzwMb2rtTB1PyLhp6oIDzwdEVXFpZybr82qI6dY qdhqVNqVGZQajM0JuApr6W1h9QIxm6pB4TP+Vqr8ZjJTk3JAa2BFaWugdYDXwrM04/hs yC1BAMtjuRqQ+/q4ZpFbfGSIT0Nhwj0qhCShhEGR7GwD92W29VOOISkyZCm/50oUBGWW IB2ioSrOFcEuXgmOpHbSAQDlwnxiQf2myNuvBx1ZbCFLCcUKvAnB0aR4JctrkxIBYjc4 IaXw== X-Gm-Message-State: AC+VfDz9Png6CZZSIhZga5xqkhuxeDUvmPIj2yA0pYsqG5GLsYX0+vH1 A1piSGfaubDWujB4g8oevtE= X-Google-Smtp-Source: ACHHUZ5KL2dkTrDBHB5xFhsizQ21blEeXqp67Pe2LQdYDiY/iIvys/JkvRO5W6BkaVZJEHCTVOZdKQ== X-Received: by 2002:a05:6a20:9191:b0:113:fe95:da8c with SMTP id v17-20020a056a20919100b00113fe95da8cmr712667pzd.14.1686086762296; Tue, 06 Jun 2023 14:26:02 -0700 (PDT) Received: from V92F7Y9K0C.corp.robot.car ([199.73.127.2]) by smtp.gmail.com with ESMTPSA id 12-20020a170902c24c00b001afebec96basm8992514plg.148.2023.06.06.14.26.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Jun 2023 14:26:01 -0700 (PDT) Date: Tue, 6 Jun 2023 14:25:56 -0700 From: Dennis Zhou To: "Liam R. Howlett" Cc: Yu Ma , akpm@linux-foundation.org, tim.c.chen@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, dave.hansen@intel.com, dan.j.williams@intel.com, shakeelb@google.com, pan.deng@intel.com, tianyou.li@intel.com, lipeng.zhu@intel.com, tim.c.chen@linux.intel.com Subject: Re: [PATCH] percpu-internal/pcpu_chunk: Re-layout pcpu_chunk structure to reduce false sharing Message-ID: References: <20230606125404.95256-1-yu.ma@intel.com> <20230606192127.w66indpq74ec6eyt@revolver> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230606192127.w66indpq74ec6eyt@revolver> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Tue, Jun 06, 2023 at 03:21:27PM -0400, Liam R. Howlett wrote: > * Yu Ma [230606 08:27]: > > When running UnixBench/Execl throughput case, false sharing is observed > > due to frequent read on base_addr and write on free_bytes, chunk_md. > > > > UnixBench/Execl represents a class of workload where bash scripts > > are spawned frequently to do some short jobs. It will do system call on > > execl frequently, and execl will call mm_init to initialize mm_struct > > of the process. mm_init will call __percpu_counter_init for > > percpu_counters initialization. Then pcpu_alloc is called to read > > the base_addr of pcpu_chunk for memory allocation. Inside pcpu_alloc, > > it will call pcpu_alloc_area to allocate memory from a specified chunk. > > This function will update "free_bytes" and "chunk_md" to record the > > rest free bytes and other meta data for this chunk. Correspondingly, > > pcpu_free_area will also update these 2 members when free memory. > > Call trace from perf is as below: > > + 57.15% 0.01% execl [kernel.kallsyms] [k] __percpu_counter_init > > + 57.13% 0.91% execl [kernel.kallsyms] [k] pcpu_alloc > > - 55.27% 54.51% execl [kernel.kallsyms] [k] osq_lock > > - 53.54% 0x654278696e552f34 > > main > > __execve > > entry_SYSCALL_64_after_hwframe > > do_syscall_64 > > __x64_sys_execve > > do_execveat_common.isra.47 > > alloc_bprm > > mm_init > > __percpu_counter_init > > pcpu_alloc > > - __mutex_lock.isra.17 > > > > In current pcpu_chunk layout, ‘base_addr’ is in the same cache line > > with ‘free_bytes’ and ‘chunk_md’, and ‘base_addr’ is at the > > last 8 bytes. This patch moves ‘bound_map’ up to ‘base_addr’, > > to let ‘base_addr’ locate in a new cacheline. > > > > With this change, on Intel Sapphire Rapids 112C/224T platform, > > based on v6.4-rc4, the 160 parallel score improves by 24%. > > Can we have a comment somewhere around this structure to avoid someone > reverting this change by accident? > I agree with Liam. It was only recently percpu was added to the mm_struct so this wasn't originally on the hot path. It's probably worth reshuffling around pcpu_chunk because as you point out base_addr is read_only after init. There in general aren't that many of these structs on any particular host, so its probably good to just annotate with ____cacheline_aligned_in_smp and potentially reshuffle around a few other variables. Another optimization here is a batch allocation which hasn't been done yet (allocate essentially an array of percpu variables all at once, but allow for their lifetimes to be independent). PS - I know I'm not super active, but please cc me on percpu changes. Thanks, Dennis > > > > Reviewed-by: Tim Chen > > Signed-off-by: Yu Ma > > --- > > mm/percpu-internal.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h > > index f9847c131998..981eeb2ad0a9 100644 > > --- a/mm/percpu-internal.h > > +++ b/mm/percpu-internal.h > > @@ -41,10 +41,10 @@ struct pcpu_chunk { > > struct list_head list; /* linked to pcpu_slot lists */ > > int free_bytes; /* free bytes in the chunk */ > > struct pcpu_block_md chunk_md; > > + unsigned long *bound_map; /* boundary map */ > > void *base_addr; /* base address of this chunk */ > > > > unsigned long *alloc_map; /* allocation map */ > > - unsigned long *bound_map; /* boundary map */ > > struct pcpu_block_md *md_blocks; /* metadata blocks */ > > > > void *data; /* chunk data */ > > -- > > 2.39.3 > > >