From patchwork Thu Aug 10 18:34:45 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Rafael J. Wysocki" X-Patchwork-Id: 712507 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 F3279C001DE for ; Thu, 10 Aug 2023 18:40:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235880AbjHJSkM (ORCPT ); Thu, 10 Aug 2023 14:40:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236086AbjHJSjn (ORCPT ); Thu, 10 Aug 2023 14:39:43 -0400 Received: from cloudserver094114.home.pl (cloudserver094114.home.pl [79.96.170.134]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DCEFF30E9; Thu, 10 Aug 2023 11:39:03 -0700 (PDT) Received: from localhost (127.0.0.1) (HELO v370.home.net.pl) by /usr/run/smtp (/usr/run/postfix/private/idea_relay_lmtp) via UNIX with SMTP (IdeaSmtpServer 5.2.0) id 6a932c9c04ad06ea; Thu, 10 Aug 2023 20:38:24 +0200 Authentication-Results: v370.home.net.pl; spf=softfail (domain owner discourages use of this host) smtp.mailfrom=rjwysocki.net (client-ip=195.136.19.94; helo=[195.136.19.94]; envelope-from=rjw@rjwysocki.net; receiver=) Received: from kreacher.localnet (unknown [195.136.19.94]) (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 v370.home.net.pl (Postfix) with ESMTPSA id 5787066275F; Thu, 10 Aug 2023 20:38:23 +0200 (CEST) From: "Rafael J. Wysocki" To: Linux PM , Anna-Maria Behnsen , Doug Smythies Cc: Peter Zijlstra , LKML , Frederic Weisbecker , Kajetan Puchalski , Srinivas Pandruvada Subject: [RFT] [PATCH v2] cpuidle: menu: Skip tick_nohz_get_sleep_length() call in some cases Date: Thu, 10 Aug 2023 20:34:45 +0200 Message-ID: <12275372.O9o76ZdvQC@kreacher> MIME-Version: 1.0 X-CLIENT-IP: 195.136.19.94 X-CLIENT-HOSTNAME: 195.136.19.94 X-VADE-SPAMSTATE: clean X-VADE-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedviedrleeigdduvdeiucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecujffqoffgrffnpdggtffipffknecuuegrihhlohhuthemucduhedtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpefhvfevufffkfgggfgtsehtufertddttdejnecuhfhrohhmpedftfgrfhgrvghlucflrdcuhgihshhotghkihdfuceorhhjfiesrhhjfiihshhotghkihdrnhgvtheqnecuggftrfgrthhtvghrnhepffffffekgfehheffleetieevfeefvefhleetjedvvdeijeejledvieehueevueffnecukfhppeduleehrddufeeirdduledrleegnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehinhgvthepudelhedrudefiedrudelrdelgedphhgvlhhopehkrhgvrggthhgvrhdrlhhotggrlhhnvghtpdhmrghilhhfrhhomhepfdftrghfrggvlhculfdrucghhihsohgtkhhifdcuoehrjhifsehrjhifhihsohgtkhhirdhnvghtqedpnhgspghrtghpthhtohepkedprhgtphhtthhopehlihhnuhigqdhpmhesvhhgvghrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopegrnhhnrgdqmhgrrhhirgeslhhinhhuthhrohhnihigrdguvgdprhgtphhtthhopegushhmhihthhhivghssehtvghluhhsrdhnvghtpdhrtghpthhtohepphgvthgvrhiisehinhhfrhgruggvrggurdhorhhgpdhrtghpthhtoheplhhinhhugidqkhgvrhhnvghlsehv ghgvrhdrkhgvrhhnvghlrdhorhhgpdhrtghpthhtohepfhhrvgguvghrihgtsehkvghrnhgvlhdrohhrgh X-DCC--Metrics: v370.home.net.pl 1024; Body=8 Fuz1=8 Fuz2=8 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org From: Rafael J. Wysocki Subject: [PATCH] cpuidle: menu: Skip tick_nohz_get_sleep_length() call in some cases Because the cost of calling tick_nohz_get_sleep_length() may increase in the future, reorder the code in menu_select() so it first uses the statistics to determine the expected idle duration. If that value is higher than RESIDENCY_THRESHOLD_NS, tick_nohz_get_sleep_length() will be called to obtain the time till the closest timer and refine the idle duration prediction if necessary. This causes the governor to always take the full overhead of get_typical_interval() with the assumption that the cost will be amortized by skipping the tick_nohz_get_sleep_length() call in the cases when the predicted idle duration is relatively very small. Signed-off-by: Rafael J. Wysocki --- v1 -> v2: Add missing max check to get_typical_interval(). --- drivers/cpuidle/governors/gov.h | 14 ++++++++ drivers/cpuidle/governors/menu.c | 65 ++++++++++++++++++++++----------------- drivers/cpuidle/governors/teo.c | 9 +---- 3 files changed, 54 insertions(+), 34 deletions(-) Index: linux-pm/drivers/cpuidle/governors/menu.c =================================================================== --- linux-pm.orig/drivers/cpuidle/governors/menu.c +++ linux-pm/drivers/cpuidle/governors/menu.c @@ -19,6 +19,8 @@ #include #include +#include "gov.h" + #define BUCKETS 12 #define INTERVAL_SHIFT 3 #define INTERVALS (1UL << INTERVAL_SHIFT) @@ -166,8 +168,7 @@ static void menu_update(struct cpuidle_d * of points is below a threshold. If it is... then use the * average of these 8 points as the estimated value. */ -static unsigned int get_typical_interval(struct menu_device *data, - unsigned int predicted_us) +static unsigned int get_typical_interval(struct menu_device *data) { int i, divisor; unsigned int min, max, thresh, avg; @@ -195,11 +196,7 @@ again: } } - /* - * If the result of the computation is going to be discarded anyway, - * avoid the computation altogether. - */ - if (min >= predicted_us) + if (!max) return UINT_MAX; if (divisor == INTERVALS) @@ -267,7 +264,6 @@ static int menu_select(struct cpuidle_dr { struct menu_device *data = this_cpu_ptr(&menu_devices); s64 latency_req = cpuidle_governor_latency_req(dev->cpu); - unsigned int predicted_us; u64 predicted_ns; u64 interactivity_req; unsigned int nr_iowaiters; @@ -279,16 +275,41 @@ static int menu_select(struct cpuidle_dr data->needs_update = 0; } - /* determine the expected residency time, round up */ - delta = tick_nohz_get_sleep_length(&delta_tick); - if (unlikely(delta < 0)) { - delta = 0; - delta_tick = 0; - } - data->next_timer_ns = delta; - nr_iowaiters = nr_iowait_cpu(dev->cpu); - data->bucket = which_bucket(data->next_timer_ns, nr_iowaiters); + + /* Find the shortest expected idle interval. */ + predicted_ns = get_typical_interval(data) * NSEC_PER_USEC; + if (predicted_ns > RESIDENCY_THRESHOLD_NS) { + unsigned int timer_us; + + /* Determine the time till the closest timer. */ + delta = tick_nohz_get_sleep_length(&delta_tick); + if (unlikely(delta < 0)) { + delta = 0; + delta_tick = 0; + } + + data->next_timer_ns = delta; + data->bucket = which_bucket(data->next_timer_ns, nr_iowaiters); + + /* Round up the result for half microseconds. */ + timer_us = div_u64((RESOLUTION * DECAY * NSEC_PER_USEC) / 2 + + data->next_timer_ns * + data->correction_factor[data->bucket], + RESOLUTION * DECAY * NSEC_PER_USEC); + /* Use the lowest expected idle interval to pick the idle state. */ + predicted_ns = min((u64)timer_us * NSEC_PER_USEC, predicted_ns); + } else { + /* + * Because the next timer event is not going to be determined + * in this case, assume that without the tick the closest timer + * will be in distant future and that the closest tick will occur + * after 1/2 of the tick period. + */ + data->next_timer_ns = KTIME_MAX; + delta_tick = TICK_NSEC / 2; + data->bucket = which_bucket(KTIME_MAX, nr_iowaiters); + } if (unlikely(drv->state_count <= 1 || latency_req == 0) || ((data->next_timer_ns < drv->states[1].target_residency_ns || @@ -303,16 +324,6 @@ static int menu_select(struct cpuidle_dr return 0; } - /* Round up the result for half microseconds. */ - predicted_us = div_u64(data->next_timer_ns * - data->correction_factor[data->bucket] + - (RESOLUTION * DECAY * NSEC_PER_USEC) / 2, - RESOLUTION * DECAY * NSEC_PER_USEC); - /* Use the lowest expected idle interval to pick the idle state. */ - predicted_ns = (u64)min(predicted_us, - get_typical_interval(data, predicted_us)) * - NSEC_PER_USEC; - if (tick_nohz_tick_stopped()) { /* * If the tick is already stopped, the cost of possible short Index: linux-pm/drivers/cpuidle/governors/gov.h =================================================================== --- /dev/null +++ linux-pm/drivers/cpuidle/governors/gov.h @@ -0,0 +1,14 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +/* Common definitions for cpuidle governors. */ + +#ifndef __CPUIDLE_GOVERNOR_H +#define __CPUIDLE_GOVERNOR_H + +/* + * Idle state target residency threshold used for deciding whether or not to + * check the time till the closest expected timer event. + */ +#define RESIDENCY_THRESHOLD_NS (15 * NSEC_PER_USEC) + +#endif /* __CPUIDLE_GOVERNOR_H */ Index: linux-pm/drivers/cpuidle/governors/teo.c =================================================================== --- linux-pm.orig/drivers/cpuidle/governors/teo.c +++ linux-pm/drivers/cpuidle/governors/teo.c @@ -140,6 +140,8 @@ #include #include +#include "gov.h" + /* * The number of bits to shift the CPU's capacity by in order to determine * the utilized threshold. @@ -152,7 +154,6 @@ */ #define UTIL_THRESHOLD_SHIFT 6 - /* * The PULSE value is added to metrics when they grow and the DECAY_SHIFT value * is used for decreasing metrics on a regular basis. @@ -166,12 +167,6 @@ */ #define NR_RECENT 9 -/* - * Idle state target residency threshold used for deciding whether or not to - * check the time till the closest expected timer event. - */ -#define RESIDENCY_THRESHOLD_NS (15 * NSEC_PER_USEC) - /** * struct teo_bin - Metrics used by the TEO cpuidle governor. * @intercepts: The "intercepts" metric.