[RFC,1/2] cpufreq: Add special-purpose fast-switching callback for drivers

Message ID	2174134.tL5yAn4CWt@kreacher (mailing list archive)
State	RFC
Headers	show Return-Path: <linux-pm-owner@kernel.org> From: "Rafael J. Wysocki" <rjw@rjwysocki.net> To: Linux PM <linux-pm@vger.kernel.org> Cc: LKML <linux-kernel@vger.kernel.org>, Viresh Kumar <viresh.kumar@linaro.org>, Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>, Doug Smythies <dsmythies@telus.net>, Giovanni Gherdovich <ggherdovich@suse.com> Subject: [RFC][PATCH 1/2] cpufreq: Add special-purpose fast-switching callback for drivers Date: Mon, 30 Nov 2020 19:37:01 +0100 Message-ID: <2174134.tL5yAn4CWt@kreacher> In-Reply-To: <1817571.2o5Kk4Ohv2@kreacher> References: <1817571.2o5Kk4Ohv2@kreacher> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Precedence: bulk
Series	cpufreq: Allow drivers to receive more information from the governor \| expand [RFC,0/2] cpufreq: Allow drivers to receive more information from the governor [RFC,1/2] cpufreq: Add special-purpose fast-switching callback for drivers [RFC,2/2] cpufreq: intel_pstate: Implement the ->adjust_perf() callback

Index: linux-pm/include/linux/cpufreq.h =================================================================== --- linux-pm.orig/include/linux/cpufreq.h +++ linux-pm/include/linux/cpufreq.h @@ -320,6 +320,15 @@ struct cpufreq_driver { unsigned int index); unsigned int (*fast_switch)(struct cpufreq_policy *policy, unsigned int target_freq); + /* + * ->fast_switch() replacement for drivers that use an internal + * representation of performance levels and can pass hints other than + * the target performance level to the hardware. + */ + void (*adjust_perf)(unsigned int cpu, bool busy, + unsigned long min_perf, + unsigned long target_perf, + unsigned long capacity); /* * Caches and returns the lowest driver-supported frequency greater than @@ -588,6 +597,11 @@ struct cpufreq_governor { /* Pass a target to the cpufreq driver */ unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy, unsigned int target_freq); +void cpufreq_driver_adjust_perf(unsigned int cpu, bool busy, + unsigned long min_perf, + unsigned long target_perf, + unsigned long capacity); +bool cpufreq_driver_has_adjust_perf(void); int cpufreq_driver_target(struct cpufreq_policy *policy, unsigned int target_freq, unsigned int relation); Index: linux-pm/drivers/cpufreq/cpufreq.c =================================================================== --- linux-pm.orig/drivers/cpufreq/cpufreq.c +++ linux-pm/drivers/cpufreq/cpufreq.c @@ -2094,6 +2094,47 @@ unsigned int cpufreq_driver_fast_switch( } EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch); +/** + * cpufreq_driver_adjust_perf - Adjust CPU performance level in one go. + * @cpu: Target CPU. + * @busy: Whether or not @CPU has been busy since the previous update. + * @min_perf: Minimum (required) performance level (units of @capacity). + * @target_perf: Terget (desired) performance level (units of @capacity). + * @capacity: Capacity of the target CPU. + * + * Carry out a fast performance level switch of @cpu without sleeping. + * + * The driver's ->adjust_perf() callback invoked by this function must be + * suitable for being called from within RCU-sched read-side critical sections + * and it is expected to select a suitable performance level equal to or above + * @min_perf and preferably equal to or below @target_perf. + * + * This function must not be called if policy->fast_switch_enabled is unset. + * + * Governors calling this function must guarantee that it will never be invoked + * twice in parallel for the same CPU and that it will never be called in + * parallel with either ->target() or ->target_index() or ->fast_switch() for + * the same CPU. + */ +void cpufreq_driver_adjust_perf(unsigned int cpu, bool busy, + unsigned long min_perf, + unsigned long target_perf, + unsigned long capacity) +{ + cpufreq_driver->adjust_perf(cpu, busy, min_perf, target_perf, capacity); +} + +/** + * cpufreq_driver_has_adjust_perf - Check "direct fast switch" callback. + * + * Return 'true' if the ->adjust_perf callback is present for the + * current driver or 'false' otherwise. + */ +bool cpufreq_driver_has_adjust_perf(void) +{ + return !!cpufreq_driver->adjust_perf; +} + /* Must set freqs->new to intermediate frequency */ static int __target_intermediate(struct cpufreq_policy *policy, struct cpufreq_freqs *freqs, int index) Index: linux-pm/kernel/sched/cpufreq_schedutil.c =================================================================== --- linux-pm.orig/kernel/sched/cpufreq_schedutil.c +++ linux-pm/kernel/sched/cpufreq_schedutil.c @@ -40,6 +40,7 @@ struct sugov_policy { struct task_struct *thread; bool work_in_progress; + bool direct_fast_switch; bool limits_changed; bool need_freq_update; }; @@ -454,6 +455,25 @@ static void sugov_update_single(struct u util = sugov_get_util(sg_cpu); max = sg_cpu->max; util = sugov_iowait_apply(sg_cpu, time, util, max); + + /* + * This code runs under rq->lock for the target CPU, so it won't run + * concurrently on two different CPUs for the same target and it is not + * necessary to acquire the lock in the fast switch case. + */ + if (sg_policy->direct_fast_switch) { + /* + * In this case, any optimizations that can be done are up to + * the driver. + */ + cpufreq_driver_adjust_perf(sg_cpu->cpu, + sugov_cpu_is_busy(sg_cpu), + map_util_perf(sg_cpu->bw_dl), + map_util_perf(util), max); + sg_policy->last_freq_update_time = time; + return; + } + next_f = get_next_freq(sg_policy, util, max); /* * Do not reduce the frequency if the CPU has not been idle @@ -466,11 +486,6 @@ static void sugov_update_single(struct u sg_policy->cached_raw_freq = cached_freq; } - /* - * This code runs under rq->lock for the target CPU, so it won't run - * concurrently on two different CPUs for the same target and it is not - * necessary to acquire the lock in the fast switch case. - */ if (sg_policy->policy->fast_switch_enabled) { sugov_fast_switch(sg_policy, time, next_f); } else { @@ -655,10 +670,6 @@ static int sugov_kthread_create(struct s struct cpufreq_policy *policy = sg_policy->policy; int ret; - /* kthread only required for slow path */ - if (policy->fast_switch_enabled) - return 0; - kthread_init_work(&sg_policy->work, sugov_work); kthread_init_worker(&sg_policy->worker); thread = kthread_create(kthread_worker_fn, &sg_policy->worker, @@ -736,9 +747,14 @@ static int sugov_init(struct cpufreq_pol goto disable_fast_switch; } - ret = sugov_kthread_create(sg_policy); - if (ret) - goto free_sg_policy; + if (policy->fast_switch_enabled) { + sg_policy->direct_fast_switch = cpufreq_driver_has_adjust_perf(); + } else { + /* kthread only required for slow path */ + ret = sugov_kthread_create(sg_policy); + if (ret) + goto free_sg_policy; + } mutex_lock(&global_tunables_lock); Index: linux-pm/include/linux/sched/cpufreq.h =================================================================== --- linux-pm.orig/include/linux/sched/cpufreq.h +++ linux-pm/include/linux/sched/cpufreq.h @@ -28,6 +28,11 @@ static inline unsigned long map_util_fre { return (freq + (freq >> 2)) * util / cap; } + +static inline unsigned long map_util_perf(unsigned long util) +{ + return util + (util >> 2); +} #endif /* CONFIG_CPU_FREQ */ #endif /* _LINUX_SCHED_CPUFREQ_H */

[RFC,1/2] cpufreq: Add special-purpose fast-switching callback for drivers

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