From patchwork Wed Feb 24 18:56:51 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Jesper Dangaard Brouer X-Patchwork-Id: 12102283 X-Patchwork-Delegate: kuba@kernel.org 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=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 26787C433DB for ; Wed, 24 Feb 2021 19:00:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C225864F19 for ; Wed, 24 Feb 2021 19:00:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230001AbhBXTAL (ORCPT ); Wed, 24 Feb 2021 14:00:11 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:32374 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235031AbhBXS60 (ORCPT ); Wed, 24 Feb 2021 13:58:26 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614193019; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=v9LQLzVj/XgMadw/p7LX8ICKSHncxAimW+HcgNIftlg=; b=KAOMUjeO/6HhWsVOAnhg8x2UkBgUf4ZIU8juOZtmoilMVEysSpfMOgJiZEQh6REhCTeh7O 7nLgohNLoW+oYL1GjC6JdajA4vcFiWjyYiHpMCJdMD9jd4EG+Gey9ANlQ5mUq8nU9H2NnO zArWIdYZt6yfi6WKqC4Rx+lA1ZzWAGI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-464-kM7Hat76MumCvQC04j4t3Q-1; Wed, 24 Feb 2021 13:56:57 -0500 X-MC-Unique: kM7Hat76MumCvQC04j4t3Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7C6431868405; Wed, 24 Feb 2021 18:56:55 +0000 (UTC) Received: from firesoul.localdomain (unknown [10.40.208.7]) by smtp.corp.redhat.com (Postfix) with ESMTP id 696C39CA0; Wed, 24 Feb 2021 18:56:52 +0000 (UTC) Received: from [192.168.42.3] (localhost [IPv6:::1]) by firesoul.localdomain (Postfix) with ESMTP id 5ACFA30736C73; Wed, 24 Feb 2021 19:56:51 +0100 (CET) Subject: [PATCH RFC net-next 3/3] mm: make zone->free_area[order] access faster From: Jesper Dangaard Brouer To: Mel Gorman , linux-mm@kvack.org Cc: Jesper Dangaard Brouer , chuck.lever@oracle.com, netdev@vger.kernel.org, linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Wed, 24 Feb 2021 19:56:51 +0100 Message-ID: <161419301128.2718959.4838557038019199822.stgit@firesoul> In-Reply-To: <161419296941.2718959.12575257358107256094.stgit@firesoul> References: <161419296941.2718959.12575257358107256094.stgit@firesoul> User-Agent: StGit/0.19 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org X-Patchwork-State: RFC Avoid multiplication (imul) operations when accessing: zone->free_area[order].nr_free This was really tricky to find. I was puzzled why perf reported that rmqueue_bulk was using 44% of the time in an imul operation: │ del_page_from_free_list(): 44,54 │ e2: imul $0x58,%rax,%rax This operation was generated (by compiler) because the struct free_area have size 88 bytes or 0x58 hex. The compiler cannot find a shift operation to use and instead choose to use a more expensive imul, to find the offset into the array free_area[]. The patch align struct free_area to a cache-line, which cause the compiler avoid the imul operation. The imul operation is very fast on modern Intel CPUs. To help fast-path that decrement 'nr_free' move the member 'nr_free' to be first element, which saves one 'add' operation. Looking up instruction latency this exchange a 3-cycle imul with a 1-cycle shl, saving 2-cycles. It does trade some space to do this. Used: gcc (GCC) 9.3.1 20200408 (Red Hat 9.3.1-2) Signed-off-by: Jesper Dangaard Brouer --- include/linux/mmzone.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index b593316bff3d..4d83201717e1 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -93,10 +93,12 @@ extern int page_group_by_mobility_disabled; #define get_pageblock_migratetype(page) \ get_pfnblock_flags_mask(page, page_to_pfn(page), MIGRATETYPE_MASK) +/* Aligned struct to make zone->free_area[order] access faster */ struct free_area { - struct list_head free_list[MIGRATE_TYPES]; unsigned long nr_free; -}; + unsigned long __pad_to_align_free_list; + struct list_head free_list[MIGRATE_TYPES]; +} ____cacheline_aligned_in_smp; static inline struct page *get_page_from_free_area(struct free_area *area, int migratetype)