From eaa2c3aeef83f096cd1ec73df1310712e423337b Mon Sep 17 00:00:00 2001 From: Akshay Adiga Date: Tue, 19 Apr 2016 15:28:01 +0530 Subject: cpufreq: powernv: Ramp-down global pstate slower than local-pstate The frequency transition latency from pmin to pmax is observed to be in few millisecond granurality. And it usually happens to take a performance penalty during sudden frequency rampup requests. This patch set solves this problem by using an entity called "global pstates". The global pstate is a Chip-level entity, so the global entitiy (Voltage) is managed across the cores. The local pstate is a Core-level entity, so the local entity (frequency) is managed across threads. This patch brings down global pstate at a slower rate than the local pstate. Hence by holding global pstates higher than local pstate makes the subsequent rampups faster. A per policy structure is maintained to keep track of the global and local pstate changes. The global pstate is brought down using a parabolic equation. The ramp down time to pmin is set to ~5 seconds. To make sure that the global pstates are dropped at regular interval , a timer is queued for every 2 seconds during ramp-down phase, which eventually brings the pstate down to local pstate. Iozone results show fairly consistent performance boost. YCSB on redis shows improved Max latencies in most cases. Iozone write/rewite test were made with filesizes 200704Kb and 401408Kb with different record sizes . The following table shows IOoperations/sec with and without patch. Iozone Results ( in op/sec) ( mean over 3 iterations ) --------------------------------------------------------------------- file size- with without % recordsize-IOtype patch patch change ---------------------------------------------------------------------- 200704-1-SeqWrite 1616532 1615425 0.06 200704-1-Rewrite 2423195 2303130 5.21 200704-2-SeqWrite 1628577 1602620 1.61 200704-2-Rewrite 2428264 2312154 5.02 200704-4-SeqWrite 1617605 1617182 0.02 200704-4-Rewrite 2430524 2351238 3.37 200704-8-SeqWrite 1629478 1600436 1.81 200704-8-Rewrite 2415308 2298136 5.09 200704-16-SeqWrite 1619632 1618250 0.08 200704-16-Rewrite 2396650 2352591 1.87 200704-32-SeqWrite 1632544 1598083 2.15 200704-32-Rewrite 2425119 2329743 4.09 200704-64-SeqWrite 1617812 1617235 0.03 200704-64-Rewrite 2402021 2321080 3.48 200704-128-SeqWrite 1631998 1600256 1.98 200704-128-Rewrite 2422389 2304954 5.09 200704-256 SeqWrite 1617065 1616962 0.00 200704-256-Rewrite 2432539 2301980 5.67 200704-512-SeqWrite 1632599 1598656 2.12 200704-512-Rewrite 2429270 2323676 4.54 200704-1024-SeqWrite 1618758 1616156 0.16 200704-1024-Rewrite 2431631 2315889 4.99 401408-1-SeqWrite 1631479 1608132 1.45 401408-1-Rewrite 2501550 2459409 1.71 401408-2-SeqWrite 1617095 1626069 -0.55 401408-2-Rewrite 2507557 2443621 2.61 401408-4-SeqWrite 1629601 1611869 1.10 401408-4-Rewrite 2505909 2462098 1.77 401408-8-SeqWrite 1617110 1626968 -0.60 401408-8-Rewrite 2512244 2456827 2.25 401408-16-SeqWrite 1632609 1609603 1.42 401408-16-Rewrite 2500792 2451405 2.01 401408-32-SeqWrite 1619294 1628167 -0.54 401408-32-Rewrite 2510115 2451292 2.39 401408-64-SeqWrite 1632709 1603746 1.80 401408-64-Rewrite 2506692 2433186 3.02 401408-128-SeqWrite 1619284 1627461 -0.50 401408-128-Rewrite 2518698 2453361 2.66 401408-256-SeqWrite 1634022 1610681 1.44 401408-256-Rewrite 2509987 2446328 2.60 401408-512-SeqWrite 1617524 1628016 -0.64 401408-512-Rewrite 2504409 2442899 2.51 401408-1024-SeqWrite 1629812 1611566 1.13 401408-1024-Rewrite 2507620 2442968 2.64 Tested with YCSB workload (50% update + 50% read) over redis for 1 million records and 1 million operation. Each test was carried out with target operations per second and persistence disabled. Max-latency (in us)( mean over 5 iterations ) --------------------------------------------------------------- op/s Operation with patch without patch %change --------------------------------------------------------------- 15000 Read 61480.6 50261.4 22.32 15000 cleanup 215.2 293.6 -26.70 15000 update 25666.2 25163.8 2.00 25000 Read 32626.2 89525.4 -63.56 25000 cleanup 292.2 263.0 11.10 25000 update 32293.4 90255.0 -64.22 35000 Read 34783.0 33119.0 5.02 35000 cleanup 321.2 395.8 -18.8 35000 update 36047.0 38747.8 -6.97 40000 Read 38562.2 42357.4 -8.96 40000 cleanup 371.8 384.6 -3.33 40000 update 27861.4 41547.8 -32.94 45000 Read 42271.0 88120.6 -52.03 45000 cleanup 263.6 383.0 -31.17 45000 update 29755.8 81359.0 -63.43 (test without target op/s) 47659 Read 83061.4 136440.6 -39.12 47659 cleanup 195.8 193.8 1.03 47659 update 73429.4 124971.8 -41.24 Signed-off-by: Akshay Adiga Reviewed-by: Gautham R. Shenoy Acked-by: Viresh Kumar Signed-off-by: Rafael J. Wysocki diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c index e2e2219..144c732 100644 --- a/drivers/cpufreq/powernv-cpufreq.c +++ b/drivers/cpufreq/powernv-cpufreq.c @@ -36,12 +36,56 @@ #include #include /* Required for cpu_sibling_mask() in UP configs */ #include +#include #define POWERNV_MAX_PSTATES 256 #define PMSR_PSAFE_ENABLE (1UL << 30) #define PMSR_SPR_EM_DISABLE (1UL << 31) #define PMSR_MAX(x) ((x >> 32) & 0xFF) +#define MAX_RAMP_DOWN_TIME 5120 +/* + * On an idle system we want the global pstate to ramp-down from max value to + * min over a span of ~5 secs. Also we want it to initially ramp-down slowly and + * then ramp-down rapidly later on. + * + * This gives a percentage rampdown for time elapsed in milliseconds. + * ramp_down_percentage = ((ms * ms) >> 18) + * ~= 3.8 * (sec * sec) + * + * At 0 ms ramp_down_percent = 0 + * At 5120 ms ramp_down_percent = 100 + */ +#define ramp_down_percent(time) ((time * time) >> 18) + +/* Interval after which the timer is queued to bring down global pstate */ +#define GPSTATE_TIMER_INTERVAL 2000 + +/** + * struct global_pstate_info - Per policy data structure to maintain history of + * global pstates + * @highest_lpstate: The local pstate from which we are ramping down + * @elapsed_time: Time in ms spent in ramping down from + * highest_lpstate + * @last_sampled_time: Time from boot in ms when global pstates were + * last set + * @last_lpstate,last_gpstate: Last set values for local and global pstates + * @timer: Is used for ramping down if cpu goes idle for + * a long time with global pstate held high + * @gpstate_lock: A spinlock to maintain synchronization between + * routines called by the timer handler and + * governer's target_index calls + */ +struct global_pstate_info { + int highest_lpstate; + unsigned int elapsed_time; + unsigned int last_sampled_time; + int last_lpstate; + int last_gpstate; + spinlock_t gpstate_lock; + struct timer_list timer; +}; + static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1]; static bool rebooting, throttled, occ_reset; @@ -94,6 +138,17 @@ static struct powernv_pstate_info { int nr_pstates; } powernv_pstate_info; +static inline void reset_gpstates(struct cpufreq_policy *policy) +{ + struct global_pstate_info *gpstates = policy->driver_data; + + gpstates->highest_lpstate = 0; + gpstates->elapsed_time = 0; + gpstates->last_sampled_time = 0; + gpstates->last_lpstate = 0; + gpstates->last_gpstate = 0; +} + /* * Initialize the freq table based on data obtained * from the firmware passed via device-tree @@ -285,6 +340,7 @@ static inline void set_pmspr(unsigned long sprn, unsigned long val) struct powernv_smp_call_data { unsigned int freq; int pstate_id; + int gpstate_id; }; /* @@ -343,19 +399,21 @@ static unsigned int powernv_cpufreq_get(unsigned int cpu) * (struct powernv_smp_call_data *) and the pstate_id which needs to be set * on this CPU should be present in freq_data->pstate_id. */ -static void set_pstate(void *freq_data) +static void set_pstate(void *data) { unsigned long val; - unsigned long pstate_ul = - ((struct powernv_smp_call_data *) freq_data)->pstate_id; + struct powernv_smp_call_data *freq_data = data; + unsigned long pstate_ul = freq_data->pstate_id; + unsigned long gpstate_ul = freq_data->gpstate_id; val = get_pmspr(SPRN_PMCR); val = val & 0x0000FFFFFFFFFFFFULL; pstate_ul = pstate_ul & 0xFF; + gpstate_ul = gpstate_ul & 0xFF; /* Set both global(bits 56..63) and local(bits 48..55) PStates */ - val = val | (pstate_ul << 56) | (pstate_ul << 48); + val = val | (gpstate_ul << 56) | (pstate_ul << 48); pr_debug("Setting cpu %d pmcr to %016lX\n", raw_smp_processor_id(), val); @@ -424,6 +482,110 @@ next: } } +/** + * calc_global_pstate - Calculate global pstate + * @elapsed_time: Elapsed time in milliseconds + * @local_pstate: New local pstate + * @highest_lpstate: pstate from which its ramping down + * + * Finds the appropriate global pstate based on the pstate from which its + * ramping down and the time elapsed in ramping down. It follows a quadratic + * equation which ensures that it reaches ramping down to pmin in 5sec. + */ +static inline int calc_global_pstate(unsigned int elapsed_time, + int highest_lpstate, int local_pstate) +{ + int pstate_diff; + + /* + * Using ramp_down_percent we get the percentage of rampdown + * that we are expecting to be dropping. Difference between + * highest_lpstate and powernv_pstate_info.min will give a absolute + * number of how many pstates we will drop eventually by the end of + * 5 seconds, then just scale it get the number pstates to be dropped. + */ + pstate_diff = ((int)ramp_down_percent(elapsed_time) * + (highest_lpstate - powernv_pstate_info.min)) / 100; + + /* Ensure that global pstate is >= to local pstate */ + if (highest_lpstate - pstate_diff < local_pstate) + return local_pstate; + else + return highest_lpstate - pstate_diff; +} + +static inline void queue_gpstate_timer(struct global_pstate_info *gpstates) +{ + unsigned int timer_interval; + + /* + * Setting up timer to fire after GPSTATE_TIMER_INTERVAL ms, But + * if it exceeds MAX_RAMP_DOWN_TIME ms for ramp down time. + * Set timer such that it fires exactly at MAX_RAMP_DOWN_TIME + * seconds of ramp down time. + */ + if ((gpstates->elapsed_time + GPSTATE_TIMER_INTERVAL) + > MAX_RAMP_DOWN_TIME) + timer_interval = MAX_RAMP_DOWN_TIME - gpstates->elapsed_time; + else + timer_interval = GPSTATE_TIMER_INTERVAL; + + mod_timer_pinned(&gpstates->timer, jiffies + + msecs_to_jiffies(timer_interval)); +} + +/** + * gpstate_timer_handler + * + * @data: pointer to cpufreq_policy on which timer was queued + * + * This handler brings down the global pstate closer to the local pstate + * according quadratic equation. Queues a new timer if it is still not equal + * to local pstate + */ +void gpstate_timer_handler(unsigned long data) +{ + struct cpufreq_policy *policy = (struct cpufreq_policy *)data; + struct global_pstate_info *gpstates = policy->driver_data; + int gpstate_id; + unsigned int time_diff = jiffies_to_msecs(jiffies) + - gpstates->last_sampled_time; + struct powernv_smp_call_data freq_data; + + if (!spin_trylock(&gpstates->gpstate_lock)) + return; + + gpstates->last_sampled_time += time_diff; + gpstates->elapsed_time += time_diff; + freq_data.pstate_id = gpstates->last_lpstate; + + if ((gpstates->last_gpstate == freq_data.pstate_id) || + (gpstates->elapsed_time > MAX_RAMP_DOWN_TIME)) { + gpstate_id = freq_data.pstate_id; + reset_gpstates(policy); + gpstates->highest_lpstate = freq_data.pstate_id; + } else { + gpstate_id = calc_global_pstate(gpstates->elapsed_time, + gpstates->highest_lpstate, + freq_data.pstate_id); + } + + /* + * If local pstate is equal to global pstate, rampdown is over + * So timer is not required to be queued. + */ + if (gpstate_id != freq_data.pstate_id) + queue_gpstate_timer(gpstates); + + freq_data.gpstate_id = gpstate_id; + gpstates->last_gpstate = freq_data.gpstate_id; + gpstates->last_lpstate = freq_data.pstate_id; + + /* Timer may get migrated to a different cpu on cpu hot unplug */ + smp_call_function_any(policy->cpus, set_pstate, &freq_data, 1); + spin_unlock(&gpstates->gpstate_lock); +} + /* * powernv_cpufreq_target_index: Sets the frequency corresponding to * the cpufreq table entry indexed by new_index on the cpus in the @@ -433,6 +595,9 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy, unsigned int new_index) { struct powernv_smp_call_data freq_data; + unsigned int cur_msec, gpstate_id; + unsigned long flags; + struct global_pstate_info *gpstates = policy->driver_data; if (unlikely(rebooting) && new_index != get_nominal_index()) return 0; @@ -440,22 +605,70 @@ static int powernv_cpufreq_target_index(struct cpufreq_policy *policy, if (!throttled) powernv_cpufreq_throttle_check(NULL); + cur_msec = jiffies_to_msecs(get_jiffies_64()); + + spin_lock_irqsave(&gpstates->gpstate_lock, flags); freq_data.pstate_id = powernv_freqs[new_index].driver_data; + if (!gpstates->last_sampled_time) { + gpstate_id = freq_data.pstate_id; + gpstates->highest_lpstate = freq_data.pstate_id; + goto gpstates_done; + } + + if (gpstates->last_gpstate > freq_data.pstate_id) { + gpstates->elapsed_time += cur_msec - + gpstates->last_sampled_time; + + /* + * If its has been ramping down for more than MAX_RAMP_DOWN_TIME + * we should be resetting all global pstate related data. Set it + * equal to local pstate to start fresh. + */ + if (gpstates->elapsed_time > MAX_RAMP_DOWN_TIME) { + reset_gpstates(policy); + gpstates->highest_lpstate = freq_data.pstate_id; + gpstate_id = freq_data.pstate_id; + } else { + /* Elaspsed_time is less than 5 seconds, continue to rampdown */ + gpstate_id = calc_global_pstate(gpstates->elapsed_time, + gpstates->highest_lpstate, + freq_data.pstate_id); + } + } else { + reset_gpstates(policy); + gpstates->highest_lpstate = freq_data.pstate_id; + gpstate_id = freq_data.pstate_id; + } + + /* + * If local pstate is equal to global pstate, rampdown is over + * So timer is not required to be queued. + */ + if (gpstate_id != freq_data.pstate_id) + queue_gpstate_timer(gpstates); + +gpstates_done: + freq_data.gpstate_id = gpstate_id; + gpstates->last_sampled_time = cur_msec; + gpstates->last_gpstate = freq_data.gpstate_id; + gpstates->last_lpstate = freq_data.pstate_id; + /* * Use smp_call_function to send IPI and execute the * mtspr on target CPU. We could do that without IPI * if current CPU is within policy->cpus (core) */ smp_call_function_any(policy->cpus, set_pstate, &freq_data, 1); - + spin_unlock_irqrestore(&gpstates->gpstate_lock, flags); return 0; } static int powernv_cpufreq_cpu_init(struct cpufreq_policy *policy) { - int base, i; + int base, i, ret; struct kernfs_node *kn; + struct global_pstate_info *gpstates; base = cpu_first_thread_sibling(policy->cpu); @@ -475,7 +688,34 @@ static int powernv_cpufreq_cpu_init(struct cpufreq_policy *policy) } else { kernfs_put(kn); } - return cpufreq_table_validate_and_show(policy, powernv_freqs); + + gpstates = kzalloc(sizeof(*gpstates), GFP_KERNEL); + if (!gpstates) + return -ENOMEM; + + policy->driver_data = gpstates; + + /* initialize timer */ + init_timer_deferrable(&gpstates->timer); + gpstates->timer.data = (unsigned long)policy; + gpstates->timer.function = gpstate_timer_handler; + gpstates->timer.expires = jiffies + + msecs_to_jiffies(GPSTATE_TIMER_INTERVAL); + spin_lock_init(&gpstates->gpstate_lock); + ret = cpufreq_table_validate_and_show(policy, powernv_freqs); + + if (ret < 0) + kfree(policy->driver_data); + + return ret; +} + +static int powernv_cpufreq_cpu_exit(struct cpufreq_policy *policy) +{ + /* timer is deleted in cpufreq_cpu_stop() */ + kfree(policy->driver_data); + + return 0; } static int powernv_cpufreq_reboot_notifier(struct notifier_block *nb, @@ -603,15 +843,19 @@ static struct notifier_block powernv_cpufreq_opal_nb = { static void powernv_cpufreq_stop_cpu(struct cpufreq_policy *policy) { struct powernv_smp_call_data freq_data; + struct global_pstate_info *gpstates = policy->driver_data; freq_data.pstate_id = powernv_pstate_info.min; + freq_data.gpstate_id = powernv_pstate_info.min; smp_call_function_single(policy->cpu, set_pstate, &freq_data, 1); + del_timer_sync(&gpstates->timer); } static struct cpufreq_driver powernv_cpufreq_driver = { .name = "powernv-cpufreq", .flags = CPUFREQ_CONST_LOOPS, .init = powernv_cpufreq_cpu_init, + .exit = powernv_cpufreq_cpu_exit, .verify = cpufreq_generic_frequency_table_verify, .target_index = powernv_cpufreq_target_index, .get = powernv_cpufreq_get, -- cgit v0.10.2