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[92.88.182.225]) by smtp.gmail.com with ESMTPSA id t82-v6sm651579wme.30.2018.10.04.00.42.20 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 04 Oct 2018 00:42:22 -0700 (PDT) From: Daniel Lezcano To: rafael@kernel.org Cc: rjw@rjwysocki.net, linux-pm@vger.kernel.org, Peter Zijlstra , Todd Kjos , Joel Fernandes , Colin Cross , Ramesh Thomas , Mel Gorman , Ingo Molnar , "Rafael J. Wysocki" , Alex Shi , Philippe Ombredanne , Thomas Gleixner , Greg Kroah-Hartman , Kate Stewart , linux-kernel@vger.kernel.org (open list) Subject: [PATCH 2/2] cpuidle/drivers/menu: Remove get_loadavg in the performance multiplier Date: Thu, 4 Oct 2018 09:42:07 +0200 Message-Id: <1538638927-26846-2-git-send-email-daniel.lezcano@linaro.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1538638927-26846-1-git-send-email-daniel.lezcano@linaro.org> References: <1538638927-26846-1-git-send-email-daniel.lezcano@linaro.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The function get_loadavg() returns almost always zero. To be more precise, statistically speaking for a total of 1023379 times passing in the function, the load is equal to zero 1020728 times, greater than 100, 610 times, the remaining is between 0 and 5. In 2011, the get_loadavg() was removed from the Android tree because of the above [1]. At this time, the load was: unsigned long this_cpu_load(void) { struct rq *this = this_rq(); return this->cpu_load[0]; } In 2014, the code was changed by commit 372ba8cb46b2 (cpuidle: menu: Lookup CPU runqueues less) and the load is: void get_iowait_load(unsigned long *nr_waiters, unsigned long *load) { struct rq *rq = this_rq(); *nr_waiters = atomic_read(&rq->nr_iowait); *load = rq->load.weight; } with the same result. Both measurements show using the load in this code path does no matter anymore. Removing it. [1] https://android.googlesource.com/kernel/common/+/4dedd9f124703207895777ac6e91dacde0f7cc17 Cc: Peter Zijlstra Cc: Todd Kjos Cc: Joel Fernandes Cc: Colin Cross Cc: Ramesh Thomas Cc: Mel Gorman Signed-off-by: Daniel Lezcano --- drivers/cpuidle/governors/menu.c | 26 +++++++------------------- include/linux/sched/stat.h | 1 - kernel/sched/core.c | 13 ------------- 3 files changed, 7 insertions(+), 33 deletions(-) diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index e26a409..066b01f 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -135,11 +135,6 @@ struct menu_device { #define LOAD_INT(x) ((x) >> FSHIFT) #define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100) -static inline int get_loadavg(unsigned long load) -{ - return LOAD_INT(load) * 10 + LOAD_FRAC(load) / 10; -} - static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters) { int bucket = 0; @@ -173,18 +168,10 @@ static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters * to be, the higher this multiplier, and thus the higher * the barrier to go to an expensive C state. */ -static inline int performance_multiplier(unsigned long nr_iowaiters, unsigned long load) +static inline int performance_multiplier(unsigned long nr_iowaiters) { - int mult = 1; - - /* for higher loadavg, we are more reluctant */ - - mult += 2 * get_loadavg(load); - - /* for IO wait tasks (per cpu!) we add 5x each */ - mult += 10 * nr_iowaiters; - - return mult; + /* for IO wait tasks (per cpu!) we add 10x each */ + return 1 + 10 * nr_iowaiters; } static DEFINE_PER_CPU(struct menu_device, menu_devices); @@ -290,7 +277,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, int idx; unsigned int interactivity_req; unsigned int expected_interval; - unsigned long nr_iowaiters, cpu_load; + unsigned long nr_iowaiters; ktime_t delta_next; if (data->needs_update) { @@ -307,7 +294,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, /* determine the expected residency time, round up */ data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length(&delta_next)); - get_iowait_load(&nr_iowaiters, &cpu_load); + nr_iowaiters = nr_iowait_cpu(dev->cpu); data->bucket = which_bucket(data->next_timer_us, nr_iowaiters); /* @@ -359,7 +346,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, * Use the performance multiplier and the user-configurable * latency_req to determine the maximum exit latency. */ - interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load); + interactivity_req = data->predicted_us / + performance_multiplier(nr_iowaiters); if (latency_req > interactivity_req) latency_req = interactivity_req; } diff --git a/include/linux/sched/stat.h b/include/linux/sched/stat.h index 04f1321..f30954c 100644 --- a/include/linux/sched/stat.h +++ b/include/linux/sched/stat.h @@ -20,7 +20,6 @@ extern unsigned long nr_running(void); extern bool single_task_running(void); extern unsigned long nr_iowait(void); extern unsigned long nr_iowait_cpu(int cpu); -extern void get_iowait_load(unsigned long *nr_waiters, unsigned long *load); static inline int sched_info_on(void) { diff --git a/kernel/sched/core.c b/kernel/sched/core.c index b88a145..5605f03 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2873,25 +2873,12 @@ unsigned long long nr_context_switches(void) return sum; } -/* - * Consumers of these two interfaces, like for example the cpufreq menu - * governor are using nonsensical data. Boosting frequency for a CPU that has - * IO-wait which might not even end up running the task when it does become - * runnable. - */ unsigned long nr_iowait_cpu(int cpu) { return atomic_read(&cpu_rq(cpu)->nr_iowait); } -void get_iowait_load(unsigned long *nr_waiters, unsigned long *load) -{ - struct rq *rq = this_rq(); - *nr_waiters = atomic_read(&rq->nr_iowait); - *load = rq->load.weight; -} - /* * IO-wait accounting, and how its mostly bollocks (on SMP). * -- 2.7.4