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=-5.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 6311BC4321A for ; Fri, 28 Jun 2019 01:10:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3059D216E3 for ; Fri, 28 Jun 2019 01:10:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561684220; bh=yzoO61EJmprVWNY3EpL3GXI+joDNjs4U10vKsbjnU54=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=GaJWPUm3bxZTHv2iiAVncXE+Kw6XKHF4kgTnkoORfPdRz/Sf5j8aUtZ98nwy+k7/T OSfhhDBQZ1z9agVsYWIP4uLlCXBXl0VAaKGDDie+grpLN6LCi6AJM1DrUt4T/aLvfZ kkMrOkB4ttjWU4Utk6RbDLgzK1Bpp8UEd92wNZOE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726708AbfF1BKS (ORCPT ); Thu, 27 Jun 2019 21:10:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:46514 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726595AbfF1BKS (ORCPT ); Thu, 27 Jun 2019 21:10:18 -0400 Received: from localhost (lfbn-ncy-1-174-150.w83-194.abo.wanadoo.fr [83.194.254.150]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D5D90208CB; Fri, 28 Jun 2019 01:10:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561684217; bh=yzoO61EJmprVWNY3EpL3GXI+joDNjs4U10vKsbjnU54=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=J4DAc2GS3ltAyGnSJz8KKcoypxlm0zXtV8PZB8uJEmQnyghsKWeED0zUoAfSMzoDJ DuYlTiFcwxXIiBb+vuD+HIEZiXLmpZi5D3ZmcMriTX/hUU7aa2nnD/hKhlbI+OCapN 2Lp28nmbcieceEy6Ow52Y+n5cu3oTFJwr6bK2gXY= Date: Fri, 28 Jun 2019 03:10:13 +0200 From: Frederic Weisbecker To: Wanpeng Li Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Ingo Molnar , Thomas Gleixner Subject: Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() Message-ID: <20190628011012.GA19488@lerouge> References: <1561682593-12071-1-git-send-email-wanpengli@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1561682593-12071-1-git-send-email-wanpengli@tencent.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 28, 2019 at 08:43:12AM +0800, Wanpeng Li wrote: > From: Wanpeng Li > > On a machine, cpu 0 is used for housekeeping, the other 39 cpus in the > same socket are in nohz_full mode. We can observe huge time burn in the > loop for seaching nearest busy housekeeper cpu by ftrace. > > 2) | get_nohz_timer_target() { > 2) 0.240 us | housekeeping_test_cpu(); > 2) 0.458 us | housekeeping_test_cpu(); > > ... > > 2) 0.292 us | housekeeping_test_cpu(); > 2) 0.240 us | housekeeping_test_cpu(); > 2) 0.227 us | housekeeping_any_cpu(); > 2) + 43.460 us | } > > This patch optimizes the searching logic by finding a nearest housekeeper > cpu in the housekeeping cpumask, it can minimize the worst searching time > from ~44us to < 10us in my testing. In addition, the last iterated busy > housekeeper can become a random candidate while current CPU is a better > fallback if it is a housekeeper. > > Cc: Ingo Molnar > Cc: Peter Zijlstra > Cc: Frederic Weisbecker > Cc: Thomas Gleixner > Signed-off-by: Wanpeng Li Reviewed-by: Frederic Weisbecker Thanks!