From nobody Wed Dec 31 08:30:30 2025 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 0EB3AC4332F for ; Mon, 6 Nov 2023 21:07:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233088AbjKFVHE (ORCPT ); Mon, 6 Nov 2023 16:07:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56966 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233069AbjKFVHB (ORCPT ); Mon, 6 Nov 2023 16:07:01 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1F668D78 for ; Mon, 6 Nov 2023 13:06:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1699304773; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XmQVU6t74ex4eso68OgbidZVE99nykXUpQNQesplaTI=; b=Vuj+fMfO0up3UOfyeYBZObUGeidF1Z6QqupBtbwNxabgwNiiVScvJGqKQ9jM6KNs/+Y/zf o2NJOL70KMslc4wo8mD3hAoFgR7zXDyCznmUgejx+iTR5tBraVkPEG8X5VlzlVmGZzhvg4 LAWT/wEXVeBb1XGY16EZmSnkyj2YwE4= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-639-gw2tMBDePVuaeSbAcBUdnw-1; Mon, 06 Nov 2023 16:06:10 -0500 X-MC-Unique: gw2tMBDePVuaeSbAcBUdnw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B38D9845DCE; Mon, 6 Nov 2023 21:06:09 +0000 (UTC) Received: from llong.com (unknown [10.22.17.168]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4781FC1290F; Mon, 6 Nov 2023 21:06:09 +0000 (UTC) From: Waiman Long To: Tejun Heo , Zefan Li , Johannes Weiner Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Joe Mario , Sebastian Jug , Yosry Ahmed , Waiman Long Subject: [PATCH v4 3/3] cgroup: Avoid false cacheline sharing of read mostly rstat_cpu Date: Mon, 6 Nov 2023 16:05:43 -0500 Message-Id: <20231106210543.717486-4-longman@redhat.com> In-Reply-To: <20231106210543.717486-1-longman@redhat.com> References: <20231106210543.717486-1-longman@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The rstat_cpu and also rstat_css_list of the cgroup structure are read mostly variables. However, they may share the same cacheline as the subsequent rstat_flush_next and *bstat variables which can be updated frequently. That will slow down the cgroup_rstat_cpu() call which is called pretty frequently in the rstat code. Add a CACHELINE_PADDING() line in between them to avoid false cacheline sharing. A parallel kernel build on a 2-socket x86-64 server is used as the benchmarking tool for measuring the lock hold time. Below were the lock hold time frequency distribution before and after the patch: Run time Before patch After patch -------- ------------ ----------- 0-01 us 14,594,545 15,484,707 01-05 us 439,926 207,382 05-10 us 5,960 3,174 10-15 us 3,543 3,006 15-20 us 1,397 1,066 20-25 us 25 15 25-30 us 12 10 It can be seen that the patch further pushes the lock hold time towards the lower end. Signed-off-by: Waiman Long --- include/linux/cgroup-defs.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index ff4b4c590f32..a4adc0580135 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -491,6 +491,13 @@ struct cgroup { struct cgroup_rstat_cpu __percpu *rstat_cpu; struct list_head rstat_css_list; =20 + /* + * Add padding to separate the read mostly rstat_cpu and + * rstat_css_list into a different cacheline from the following + * rstat_flush_next and *bstat fields which can have frequent updates. + */ + CACHELINE_PADDING(_pad_); + /* * A singly-linked list of cgroup structures to be rstat flushed. * This is a scratch field to be used exclusively by --=20 2.39.3