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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 942ECC47095 for ; Tue, 6 Oct 2020 19:29:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4FEED205F4 for ; Tue, 6 Oct 2020 19:29:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727128AbgJFT3e (ORCPT ); Tue, 6 Oct 2020 15:29:34 -0400 Received: from mga17.intel.com ([192.55.52.151]:34507 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727060AbgJFT3c (ORCPT ); Tue, 6 Oct 2020 15:29:32 -0400 IronPort-SDR: HAVbOduw97hmwxpVbbpwWOGHVJNXAWiW8gqcCRn9E3sg9w5tl43UknEaHGqgMaLWSPxQQ3IA4B q36MroSpyqyw== X-IronPort-AV: E=McAfee;i="6000,8403,9766"; a="144558066" X-IronPort-AV: E=Sophos;i="5.77,343,1596524400"; d="scan'208";a="144558066" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Oct 2020 12:29:28 -0700 IronPort-SDR: 9STah4YN+/SAOPpnOT7ONANbOSoP4V3o8cJ+unULqsQqDz8KGRsSizJ49TGiFYqkXKUmL4HSQz cVjbd5emwLoA== X-IronPort-AV: E=Sophos;i="5.77,343,1596524400"; d="scan'208";a="527530045" Received: from rjwysock-mobl1.ger.corp.intel.com (HELO [10.249.144.70]) ([10.249.144.70]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Oct 2020 12:29:26 -0700 Subject: Re: ACPI _CST introduced performance regresions on Haswll To: Mel Gorman Cc: Takashi Iwai , linux-kernel@vger.kernel.org References: <20201006083639.GJ3227@techsingularity.net> <20201006190322.GL3227@techsingularity.net> From: "Rafael J. Wysocki" Organization: Intel Technology Poland Sp. z o. o., KRS 101882, ul. Slowackiego 173, 80-298 Gdansk Message-ID: <25f31d3e-7a67-935f-93ba-32216a5084e2@intel.com> Date: Tue, 6 Oct 2020 21:29:24 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 In-Reply-To: <20201006190322.GL3227@techsingularity.net> Content-Type: text/plain; charset=iso-8859-15; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/6/2020 9:03 PM, Mel Gorman wrote: > On Tue, Oct 06, 2020 at 06:00:18PM +0200, Rafael J. Wysocki wrote: >>> server systems") and enable-cst is the commit. It was not fixed by 5.6 or >>> 5.9-rc8. A lot of bisections ended up here including kernel compilation, >>> tbench, syscall entry/exit microbenchmark, hackbench, Java workloads etc. >>> >>> What I don't understand is why. The latencies for c-state exit states >>> before and after the patch are both as follows >>> >>> /sys/devices/system/cpu/cpu0/cpuidle/state0/latency:0 >>> /sys/devices/system/cpu/cpu0/cpuidle/state1/latency:2 >>> /sys/devices/system/cpu/cpu0/cpuidle/state2/latency:10 >>> /sys/devices/system/cpu/cpu0/cpuidle/state3/latency:33 >>> /sys/devices/system/cpu/cpu0/cpuidle/state4/latency:133 >>> >>> Perf profiles did not show up anything interesting. A diff of >>> /sys/devices/system/cpu/cpu0/cpuidle/state0/ before and after the patch >>> showed up nothing interesting. Any idea why exactly this patch shows up >>> as being hazardous on Haswell in particular? >>> >> Presumably, some of the idle states are disabled by default on the affected >> machines. >> >> Can you check the disable and default_status attributes of each state before >> and after the commit in question? >> > # grep . pre-cst/cpuidle/state*/disable > pre-cst/cpuidle/state0/disable:0 > pre-cst/cpuidle/state1/disable:0 > pre-cst/cpuidle/state2/disable:0 > pre-cst/cpuidle/state3/disable:0 > pre-cst/cpuidle/state4/disable:0 > # grep . enable-cst/cpuidle/state*/disable > enable-cst/cpuidle/state0/disable:0 > enable-cst/cpuidle/state1/disable:0 > enable-cst/cpuidle/state2/disable:0 > enable-cst/cpuidle/state3/disable:0 > enable-cst/cpuidle/state4/disable:0 > # grep . pre-cst/cpuidle/state*/default_status > pre-cst/cpuidle/state0/default_status:enabled > pre-cst/cpuidle/state1/default_status:enabled > pre-cst/cpuidle/state2/default_status:enabled > pre-cst/cpuidle/state3/default_status:enabled > pre-cst/cpuidle/state4/default_status:enabled > > After the commit, the default_status file does not appear in /sys > Something is amiss, then, because the commit doesn't affect the presence of this file. The only thing it does is to set the use_acpi flag for several processor models in intel_idle.c. It can be effectively reversed by removing all of the ".use_acpi = true," lines from intel_idle.c. In particular, please check if changing the value of use_acpi in struct idle_cpu_hsx from 'true' to 'false' alone (without reverting the commit) makes the issue go away in 5.9-rc8 (the default_status file should be present regardless). Cheers!