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[71.255.246.27]) by smtp.gmail.com with ESMTPSA id u22sm1327743qkj.97.2020.02.13.06.05.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 13 Feb 2020 06:05:38 -0800 (PST) Subject: Re: [Patch v9 3/8] arm,arm64,drivers:Add infrastructure to store and update instantaneous thermal pressure To: Amit Kucheria References: <1580250967-4386-1-git-send-email-thara.gopinath@linaro.org> <1580250967-4386-4-git-send-email-thara.gopinath@linaro.org> Cc: Ingo Molnar , Peter Zijlstra , ionela.voinescu@arm.com, Vincent Guittot , Dietmar Eggemann , Zhang Rui , qperret@google.com, Daniel Lezcano , Viresh Kumar , Steven Rostedt , Will Deacon , Catalin Marinas , Sudeep Holla , Juri Lelli , corbet@lwn.net, LKML , Amit Daniel Kachhap , Javi Merino From: Thara Gopinath Message-ID: <5E4557B1.8020809@linaro.org> Date: Thu, 13 Feb 2020 09:05:37 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/13/2020 07:25 AM, Amit Kucheria wrote: > On Wed, Jan 29, 2020 at 4:06 AM Thara Gopinath > wrote: >> >> Add architecture specific APIs to update and track thermal pressure on a >> per cpu basis. A per cpu variable thermal_pressure is introduced to keep >> track of instantaneous per cpu thermal pressure. Thermal pressure is the >> delta between maximum capacity and capped capacity due to a thermal event. > > s/capped/decreased to have consistent use throughout the series e.g. in patch 1. > > Though personally, I like "capped capacity" in which case > s/decreased/capped in patch 1 and elsewhere. I will fix this > >> >> topology_get_thermal_pressure can be hooked into the scheduler specified >> arch_cpu_thermal_capacity to retrieve instantaneous thermal pressure of a >> cpu. >> >> arch_set_thermal_pressure can be used to update the thermal pressure. >> >> Considering topology_get_thermal_pressure reads thermal_pressure and >> arch_set_thermal_pressure writes into thermal_pressure, one can argue for >> some sort of locking mechanism to avoid a stale value. But considering >> topology_get_thermal_pressure can be called from a system critical path >> like scheduler tick function, a locking mechanism is not ideal. This means >> that it is possible the thermal_pressure value used to calculate average >> thermal pressure for a cpu can be stale for upto 1 tick period. >> >> Signed-off-by: Thara Gopinath >> --- >> >> v6->v7: >> - Changed the input argument in arch_set_thermal_pressure from >> capped capacity to delta capacity(thermal pressure) as per >> Ionela's review comments. >> >> arch/arm/include/asm/topology.h | 3 +++ >> arch/arm64/include/asm/topology.h | 3 +++ > > Any particular reason to enable this for arm/arm64 in this patch > itself? I'd have enabled them in two separate patches after this one. No reason. No reason not to as well as arch_topology is "Arm specific cpu topology file" and changes are one-liners. > >> drivers/base/arch_topology.c | 11 +++++++++++ >> include/linux/arch_topology.h | 10 ++++++++++ >> 4 files changed, 27 insertions(+) >> >> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h >> index 8a0fae9..3a50a19 100644 >> --- a/arch/arm/include/asm/topology.h >> +++ b/arch/arm/include/asm/topology.h >> @@ -16,6 +16,9 @@ >> /* Enable topology flag updates */ >> #define arch_update_cpu_topology topology_update_cpu_topology >> >> +/* Replace task scheduler's default thermal pressure retrieve API */ >> +#define arch_cpu_thermal_pressure topology_get_thermal_pressure >> + >> #else >> >> static inline void init_cpu_topology(void) { } >> diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h >> index a4d945d..a70896f 100644 >> --- a/arch/arm64/include/asm/topology.h >> +++ b/arch/arm64/include/asm/topology.h >> @@ -25,6 +25,9 @@ int pcibus_to_node(struct pci_bus *bus); >> /* Enable topology flag updates */ >> #define arch_update_cpu_topology topology_update_cpu_topology >> >> +/* Replace task scheduler's default thermal pressure retrieve API */ >> +#define arch_cpu_thermal_pressure topology_get_thermal_pressure >> + >> #include >> >> #endif /* _ASM_ARM_TOPOLOGY_H */ >> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c >> index 6119e11..68dfa49 100644 >> --- a/drivers/base/arch_topology.c >> +++ b/drivers/base/arch_topology.c >> @@ -42,6 +42,17 @@ void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity) >> per_cpu(cpu_scale, cpu) = capacity; >> } >> >> +DEFINE_PER_CPU(unsigned long, thermal_pressure); >> + >> +void arch_set_thermal_pressure(struct cpumask *cpus, >> + unsigned long th_pressure) >> +{ >> + int cpu; > > > -- Warm Regards Thara