[3/4] arm64: topology: Tell the scheduler about the relative power of cores

Message ID	1387483575-11430-4-git-send-email-broonie@kernel.org (mailing list archive)
State	New, archived
Headers	show Return-Path: <linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org> From: Mark Brown <broonie@kernel.org> To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>, Catalin Marinas <Catalin.Marinas@arm.com>, Will Deacon <will.deacon@arm.com> Date: Thu, 19 Dec 2013 20:06:14 +0000 Message-Id: <1387483575-11430-4-git-send-email-broonie@kernel.org> In-Reply-To: <1387483575-11430-1-git-send-email-broonie@kernel.org> References: <1387483575-11430-1-git-send-email-broonie@kernel.org> Subject: [PATCH 3/4] arm64: topology: Tell the scheduler about the relative power of cores Cc: linaro-kernel@lists.linaro.org, linux-arm-kernel@lists.infradead.org, Mark Brown <broonie@linaro.org> Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" <linux-arm-kernel-bounces@lists.infradead.org> Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c index 5a2724b3d4b7..68ccf4f4f258 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -23,6 +23,29 @@ #include <asm/topology.h> +/* + * cpu power table + * This per cpu data structure describes the relative capacity of each core. + * On a heteregenous system, cores don't have the same computation capacity + * and we reflect that difference in the cpu_power field so the scheduler can + * take this difference into account during load balance. A per cpu structure + * is preferred because each CPU updates its own cpu_power field during the + * load balance except for idle cores. One idle core is selected to run the + * rebalance_domains for all idle cores and the cpu_power can be updated + * during this sequence. + */ +static DEFINE_PER_CPU(unsigned long, cpu_scale); + +unsigned long arch_scale_freq_power(struct sched_domain *sd, int cpu) +{ + return per_cpu(cpu_scale, cpu); +} + +static void set_power_scale(unsigned int cpu, unsigned long power) +{ + per_cpu(cpu_scale, cpu) = power; +} + #ifdef CONFIG_OF static int cluster_id; @@ -140,9 +163,49 @@ static void __init parse_cluster(struct device_node *cluster) cluster_id++; } +struct cpu_efficiency { + const char *compatible; + unsigned long efficiency; +}; + +/* + * Table of relative efficiency of each processors + * The efficiency value must fit in 20bit and the final + * cpu_scale value must be in the range + * 0 < cpu_scale < 3*SCHED_POWER_SCALE/2 + * in order to return at most 1 when DIV_ROUND_CLOSEST + * is used to compute the capacity of a CPU. + * Processors that are not defined in the table, + * use the default SCHED_POWER_SCALE value for cpu_scale. + */ +static const struct cpu_efficiency table_efficiency[] = { + { NULL, }, +}; + +static unsigned long *__cpu_capacity; +#define cpu_capacity(cpu) __cpu_capacity[cpu] + +static unsigned long middle_capacity = 1; + +/* + * Iterate all CPUs' descriptor in DT and compute the efficiency + * (as per table_efficiency). Also calculate a middle efficiency + * as close as possible to (max{eff_i} - min{eff_i}) / 2 + * This is later used to scale the cpu_power field such that an + * 'average' CPU is of middle power. Also see the comments near + * table_efficiency[] and update_cpu_power(). + */ static void __init parse_dt_topology(void) { + const struct cpu_efficiency *cpu_eff; struct device_node *cn; + unsigned long min_capacity = (unsigned long)(-1); + unsigned long max_capacity = 0; + unsigned long capacity = 0; + int alloc_size, cpu; + + alloc_size = nr_cpu_ids * sizeof(*__cpu_capacity); + __cpu_capacity = kzalloc(alloc_size, GFP_NOWAIT); cn = of_find_node_by_path("/cpus"); if (!cn) { @@ -158,10 +221,88 @@ static void __init parse_dt_topology(void) if (!cn) return; parse_cluster(cn); + + for_each_possible_cpu(cpu) { + const u32 *rate; + int len; + + /* Too early to use cpu->of_node */ + cn = of_get_cpu_node(cpu, NULL); + if (!cn) { + pr_err("Missing device node for CPU %d\n", cpu); + continue; + } + + /* check if the cpu is marked as "disabled", if so ignore */ + if (!of_device_is_available(cn)) + continue; + + for (cpu_eff = table_efficiency; cpu_eff->compatible; cpu_eff++) + if (of_device_is_compatible(cn, cpu_eff->compatible)) + break; + + if (cpu_eff->compatible == NULL) { + pr_warn("%s: Unknown CPU type\n", cn->full_name); + continue; + } + + rate = of_get_property(cn, "clock-frequency", &len); + if (!rate || len != 4) { + pr_err("%s: Missing clock-frequency property\n", + cn->full_name); + continue; + } + + capacity = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency; + + /* Save min capacity of the system */ + if (capacity < min_capacity) + min_capacity = capacity; + + /* Save max capacity of the system */ + if (capacity > max_capacity) + max_capacity = capacity; + + cpu_capacity(cpu) = capacity; + } + + /* If min and max capacities are equal we bypass the update of the + * cpu_scale because all CPUs have the same capacity. Otherwise, we + * compute a middle_capacity factor that will ensure that the capacity + * of an 'average' CPU of the system will be as close as possible to + * SCHED_POWER_SCALE, which is the default value, but with the + * constraint explained near table_efficiency[]. + */ + if (min_capacity == max_capacity) + return; + else if (4 * max_capacity < (3 * (max_capacity + min_capacity))) + middle_capacity = (min_capacity + max_capacity) + >> (SCHED_POWER_SHIFT+1); + else + middle_capacity = ((max_capacity / 3) + >> (SCHED_POWER_SHIFT-1)) + 1; + +} + +/* + * Look for a customed capacity of a CPU in the cpu_topo_data table during the + * boot. The update of all CPUs is in O(n^2) for heteregeneous system but the + * function returns directly for SMP system. + */ +static void update_cpu_power(unsigned int cpu) +{ + if (!cpu_capacity(cpu)) + return; + + set_power_scale(cpu, cpu_capacity(cpu) / middle_capacity); + + pr_info("CPU%u: update cpu_power %lu\n", + cpu, arch_scale_freq_power(NULL, cpu)); } #else static inline void parse_dt_topology(void) {} +static inline void update_cpu_power(unsigned int cpuid) {} #endif /* @@ -210,6 +351,8 @@ void store_cpu_topology(unsigned int cpuid) pr_info("CPU%u: No topology information configured\n", cpuid); else update_siblings_masks(cpuid); + + update_cpu_power(cpuid); } /* @@ -229,6 +372,8 @@ void __init init_cpu_topology(void) cpu_topo->socket_id = -1; cpumask_clear(&cpu_topo->core_sibling); cpumask_clear(&cpu_topo->thread_sibling); + + set_power_scale(cpu, SCHED_POWER_SCALE); } parse_dt_topology();

[3/4] arm64: topology: Tell the scheduler about the relative power of cores

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