linux-kernel - Re: [PATCH] sched/fair: check for idle core

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Date:   Wed, 21 Oct 2020 15:10:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...hat.com>,
        kernel-janitors@...r.kernel.org,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org,
        Valentin Schneider <valentin.schneider@....com>,
        Gilles Muller <Gilles.Muller@...ia.fr>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, viresh.kumar@...aro.org,
        srinivas.pandruvada@...ux.intel.com
Subject: Re: [PATCH] sched/fair: check for idle core

On Wed, Oct 21, 2020 at 02:19:50PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 21, 2020 at 01:56:55PM +0200, Julia Lawall wrote:
> > Prior to 5.8, my machine was using intel_pstate and had few background
> > tasks.  Thus the problem wasn't visible in practice.  Starting with 5.8
> > the kernel decided that intel_cpufreq would be more appropriate, which
> > introduced kworkers every 0.004 seconds on all cores.
> 
> That still doesn't make any sense. Are you running the legacy on-demand
> thing or something?
> 
> Rafael, Srinivas, Viresh, how come it defaults to that?

Does we want something like this?

---
 arch/x86/configs/i386_defconfig   | 3 +--
 arch/x86/configs/x86_64_defconfig | 3 +--
 drivers/cpufreq/Kconfig           | 7 +++++--
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/arch/x86/configs/i386_defconfig b/arch/x86/configs/i386_defconfig
index 78210793d357..c343ad459737 100644
--- a/arch/x86/configs/i386_defconfig
+++ b/arch/x86/configs/i386_defconfig
@@ -41,8 +41,7 @@ CONFIG_PM_DEBUG=y
 CONFIG_PM_TRACE_RTC=y
 CONFIG_ACPI_DOCK=y
 CONFIG_ACPI_BGRT=y
-CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE=y
-CONFIG_CPU_FREQ_GOV_ONDEMAND=y
+CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL=y
 CONFIG_X86_ACPI_CPUFREQ=y
 CONFIG_EFI_VARS=y
 CONFIG_KPROBES=y
diff --git a/arch/x86/configs/x86_64_defconfig b/arch/x86/configs/x86_64_defconfig
index 9936528e1939..23e1ea85c1ec 100644
--- a/arch/x86/configs/x86_64_defconfig
+++ b/arch/x86/configs/x86_64_defconfig
@@ -38,8 +38,7 @@ CONFIG_PM_DEBUG=y
 CONFIG_PM_TRACE_RTC=y
 CONFIG_ACPI_DOCK=y
 CONFIG_ACPI_BGRT=y
-CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE=y
-CONFIG_CPU_FREQ_GOV_ONDEMAND=y
+CONFIG_CPU_FREQ_DEFAULT_GOV_SCHEDUTIL=y
 CONFIG_X86_ACPI_CPUFREQ=y
 CONFIG_IA32_EMULATION=y
 CONFIG_EFI_VARS=y
diff --git a/drivers/cpufreq/Kconfig b/drivers/cpufreq/Kconfig
index 2c7171e0b001..8dfca6e9b836 100644
--- a/drivers/cpufreq/Kconfig
+++ b/drivers/cpufreq/Kconfig
@@ -37,8 +37,7 @@ config CPU_FREQ_STAT
 choice
 	prompt "Default CPUFreq governor"
 	default CPU_FREQ_DEFAULT_GOV_USERSPACE if ARM_SA1100_CPUFREQ || ARM_SA1110_CPUFREQ
-	default CPU_FREQ_DEFAULT_GOV_SCHEDUTIL if ARM64 || ARM
-	default CPU_FREQ_DEFAULT_GOV_SCHEDUTIL if X86_INTEL_PSTATE && SMP
+	default CPU_FREQ_DEFAULT_GOV_SCHEDUTIL if SMP
 	default CPU_FREQ_DEFAULT_GOV_PERFORMANCE
 	help
 	  This option sets which CPUFreq governor shall be loaded at
@@ -71,6 +70,7 @@ config CPU_FREQ_DEFAULT_GOV_USERSPACE
 
 config CPU_FREQ_DEFAULT_GOV_ONDEMAND
 	bool "ondemand"
+	depends on !SMP
 	select CPU_FREQ_GOV_ONDEMAND
 	select CPU_FREQ_GOV_PERFORMANCE
 	help
@@ -83,6 +83,7 @@ config CPU_FREQ_DEFAULT_GOV_ONDEMAND
 
 config CPU_FREQ_DEFAULT_GOV_CONSERVATIVE
 	bool "conservative"
+	depends on !SMP
 	select CPU_FREQ_GOV_CONSERVATIVE
 	select CPU_FREQ_GOV_PERFORMANCE
 	help
@@ -144,6 +145,7 @@ config CPU_FREQ_GOV_USERSPACE
 
 config CPU_FREQ_GOV_ONDEMAND
 	tristate "'ondemand' cpufreq policy governor"
+	depends on !SMP
 	select CPU_FREQ_GOV_COMMON
 	help
 	  'ondemand' - This driver adds a dynamic cpufreq policy governor.
@@ -163,6 +165,7 @@ config CPU_FREQ_GOV_ONDEMAND
 config CPU_FREQ_GOV_CONSERVATIVE
 	tristate "'conservative' cpufreq governor"
 	depends on CPU_FREQ
+	depends on !SMP
 	select CPU_FREQ_GOV_COMMON
 	help
 	  'conservative' - this driver is rather similar to the 'ondemand'