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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright IBM Corp. 2024
4 */
5
6#define pr_fmt(fmt) "hd: " fmt
7
8/*
9 * Hiperdispatch:
10 * Dynamically calculates the optimum number of high capacity COREs
11 * by considering the state the system is in. When hiperdispatch decides
12 * that a capacity update is necessary, it schedules a topology update.
13 * During topology updates the CPU capacities are always re-adjusted.
14 *
15 * There is two places where CPU capacities are being accessed within
16 * hiperdispatch.
17 * -> hiperdispatch's reoccuring work function reads CPU capacities to
18 * determine high capacity CPU count.
19 * -> during a topology update hiperdispatch's adjustment function
20 * updates CPU capacities.
21 * These two can run on different CPUs in parallel which can cause
22 * hiperdispatch to make wrong decisions. This can potentially cause
23 * some overhead by leading to extra rebuild_sched_domains() calls
24 * for correction. Access to capacities within hiperdispatch has to be
25 * serialized to prevent the overhead.
26 *
27 * Hiperdispatch decision making revolves around steal time.
28 * HD_STEAL_THRESHOLD value is taken as reference. Whenever steal time
29 * crosses the threshold value hiperdispatch falls back to giving high
30 * capacities to entitled CPUs. When steal time drops below the
31 * threshold boundary, hiperdispatch utilizes all CPUs by giving all
32 * of them high capacity.
33 *
34 * The theory behind HD_STEAL_THRESHOLD is related to the SMP thread
35 * performance. Comparing the throughput of;
36 * - single CORE, with N threads, running N tasks
37 * - N separate COREs running N tasks,
38 * using individual COREs for individual tasks yield better
39 * performance. This performance difference is roughly ~30% (can change
40 * between machine generations)
41 *
42 * Hiperdispatch tries to hint scheduler to use individual COREs for
43 * each task, as long as steal time on those COREs are less than 30%,
44 * therefore delaying the throughput loss caused by using SMP threads.
45 */
46
47#include <linux/cpufeature.h>
48#include <linux/cpumask.h>
49#include <linux/debugfs.h>
50#include <linux/device.h>
51#include <linux/kernel_stat.h>
52#include <linux/kstrtox.h>
53#include <linux/ktime.h>
54#include <linux/sysctl.h>
55#include <linux/types.h>
56#include <linux/workqueue.h>
57#include <asm/hiperdispatch.h>
58#include <asm/setup.h>
59#include <asm/smp.h>
60#include <asm/topology.h>
61
62#define CREATE_TRACE_POINTS
63#include <asm/trace/hiperdispatch.h>
64
65#define HD_DELAY_FACTOR (4)
66#define HD_DELAY_INTERVAL (HZ / 4)
67#define HD_STEAL_THRESHOLD 10
68#define HD_STEAL_AVG_WEIGHT 16
69
70static cpumask_t hd_vl_coremask; /* Mask containing all vertical low COREs */
71static cpumask_t hd_vmvl_cpumask; /* Mask containing vertical medium and low CPUs */
72static int hd_high_capacity_cores; /* Current CORE count with high capacity */
73static int hd_entitled_cores; /* Total vertical high and medium CORE count */
74static int hd_online_cores; /* Current online CORE count */
75
76static unsigned long hd_previous_steal; /* Previous iteration's CPU steal timer total */
77static unsigned long hd_high_time; /* Total time spent while all cpus have high capacity */
78static unsigned long hd_low_time; /* Total time spent while vl cpus have low capacity */
79static atomic64_t hd_adjustments; /* Total occurrence count of hiperdispatch adjustments */
80
81static unsigned int hd_steal_threshold = HD_STEAL_THRESHOLD;
82static unsigned int hd_delay_factor = HD_DELAY_FACTOR;
83static int hd_enabled;
84
85static void hd_capacity_work_fn(struct work_struct *work);
86static DECLARE_DELAYED_WORK(hd_capacity_work, hd_capacity_work_fn);
87
88static int hd_set_hiperdispatch_mode(int enable)
89{
90 if (!cpu_has_topology())
91 enable = 0;
92 if (hd_enabled == enable)
93 return 0;
94 hd_enabled = enable;
95 return 1;
96}
97
98void hd_reset_state(void)
99{
100 cpumask_clear(&hd_vl_coremask);
101 cpumask_clear(&hd_vmvl_cpumask);
102 hd_entitled_cores = 0;
103 hd_online_cores = 0;
104}
105
106void hd_add_core(int cpu)
107{
108 const struct cpumask *siblings;
109 int polarization;
110
111 hd_online_cores++;
112 polarization = smp_cpu_get_polarization(cpu);
113 siblings = topology_sibling_cpumask(cpu);
114 switch (polarization) {
115 case POLARIZATION_VH:
116 hd_entitled_cores++;
117 break;
118 case POLARIZATION_VM:
119 hd_entitled_cores++;
120 cpumask_or(&hd_vmvl_cpumask, &hd_vmvl_cpumask, siblings);
121 break;
122 case POLARIZATION_VL:
123 cpumask_set_cpu(cpu, &hd_vl_coremask);
124 cpumask_or(&hd_vmvl_cpumask, &hd_vmvl_cpumask, siblings);
125 break;
126 }
127}
128
129/* Serialize update and read operations of debug counters. */
130static DEFINE_MUTEX(hd_counter_mutex);
131
132static void hd_update_times(void)
133{
134 static ktime_t prev;
135 ktime_t now;
136
137 /*
138 * Check if hiperdispatch is active, if not set the prev to 0.
139 * This way it is possible to differentiate the first update iteration after
140 * enabling hiperdispatch.
141 */
142 if (hd_entitled_cores == 0 || hd_enabled == 0) {
143 prev = ktime_set(0, 0);
144 return;
145 }
146 now = ktime_get();
147 if (ktime_after(prev, 0)) {
148 if (hd_high_capacity_cores == hd_online_cores)
149 hd_high_time += ktime_ms_delta(now, prev);
150 else
151 hd_low_time += ktime_ms_delta(now, prev);
152 }
153 prev = now;
154}
155
156static void hd_update_capacities(void)
157{
158 int cpu, upscaling_cores;
159 unsigned long capacity;
160
161 upscaling_cores = hd_high_capacity_cores - hd_entitled_cores;
162 capacity = upscaling_cores > 0 ? CPU_CAPACITY_HIGH : CPU_CAPACITY_LOW;
163 hd_high_capacity_cores = hd_entitled_cores;
164 for_each_cpu(cpu, &hd_vl_coremask) {
165 smp_set_core_capacity(cpu, capacity);
166 if (capacity != CPU_CAPACITY_HIGH)
167 continue;
168 hd_high_capacity_cores++;
169 upscaling_cores--;
170 if (upscaling_cores == 0)
171 capacity = CPU_CAPACITY_LOW;
172 }
173}
174
175void hd_disable_hiperdispatch(void)
176{
177 cancel_delayed_work_sync(&hd_capacity_work);
178 hd_high_capacity_cores = hd_online_cores;
179 hd_previous_steal = 0;
180}
181
182int hd_enable_hiperdispatch(void)
183{
184 mutex_lock(&hd_counter_mutex);
185 hd_update_times();
186 mutex_unlock(&hd_counter_mutex);
187 if (hd_enabled == 0)
188 return 0;
189 if (hd_entitled_cores == 0)
190 return 0;
191 if (hd_online_cores <= hd_entitled_cores)
192 return 0;
193 mod_delayed_work(system_dfl_wq, &hd_capacity_work, HD_DELAY_INTERVAL * hd_delay_factor);
194 hd_update_capacities();
195 return 1;
196}
197
198static unsigned long hd_steal_avg(unsigned long new)
199{
200 static unsigned long steal;
201
202 steal = (steal * (HD_STEAL_AVG_WEIGHT - 1) + new) / HD_STEAL_AVG_WEIGHT;
203 return steal;
204}
205
206static unsigned long hd_calculate_steal_percentage(void)
207{
208 unsigned long time_delta, steal_delta, steal, percentage;
209 static ktime_t prev;
210 int cpus;
211 ktime_t now;
212
213 percentage = 0;
214 steal = kcpustat_field_total(CPUTIME_STEAL, &hd_vmvl_cpumask);
215 cpus = cpumask_weight(&hd_vmvl_cpumask);
216 /*
217 * If there is no vertical medium and low CPUs steal time
218 * is 0 as vertical high CPUs shouldn't experience steal time.
219 */
220 if (cpus == 0)
221 return percentage;
222 now = ktime_get();
223 time_delta = ktime_to_ns(ktime_sub(now, prev));
224 if (steal > hd_previous_steal && hd_previous_steal != 0) {
225 steal_delta = (steal - hd_previous_steal) * 100 / time_delta;
226 percentage = steal_delta / cpus;
227 }
228 hd_previous_steal = steal;
229 prev = now;
230 return percentage;
231}
232
233static void hd_capacity_work_fn(struct work_struct *work)
234{
235 unsigned long steal_percentage, new_cores;
236
237 mutex_lock(&smp_cpu_state_mutex);
238 /*
239 * If online cores are less or equal to entitled cores hiperdispatch
240 * does not need to make any adjustments, call a topology update to
241 * disable hiperdispatch.
242 * Normally this check is handled on topology update, but during cpu
243 * unhotplug, topology and cpu mask updates are done in reverse
244 * order, causing hd_enable_hiperdispatch() to get stale data.
245 */
246 if (hd_online_cores <= hd_entitled_cores) {
247 topology_schedule_update();
248 mutex_unlock(&smp_cpu_state_mutex);
249 return;
250 }
251 steal_percentage = hd_steal_avg(hd_calculate_steal_percentage());
252 if (steal_percentage < hd_steal_threshold)
253 new_cores = hd_online_cores;
254 else
255 new_cores = hd_entitled_cores;
256 if (hd_high_capacity_cores != new_cores) {
257 trace_s390_hd_rebuild_domains(hd_high_capacity_cores, new_cores);
258 hd_high_capacity_cores = new_cores;
259 atomic64_inc(&hd_adjustments);
260 topology_schedule_update();
261 }
262 trace_s390_hd_work_fn(steal_percentage, hd_entitled_cores, hd_high_capacity_cores);
263 mutex_unlock(&smp_cpu_state_mutex);
264 queue_delayed_work(system_dfl_wq, &hd_capacity_work, HD_DELAY_INTERVAL);
265}
266
267static int hiperdispatch_ctl_handler(const struct ctl_table *ctl, int write,
268 void *buffer, size_t *lenp, loff_t *ppos)
269{
270 int hiperdispatch;
271 int rc;
272 struct ctl_table ctl_entry = {
273 .procname = ctl->procname,
274 .data = &hiperdispatch,
275 .maxlen = sizeof(int),
276 .extra1 = SYSCTL_ZERO,
277 .extra2 = SYSCTL_ONE,
278 };
279
280 hiperdispatch = hd_enabled;
281 rc = proc_douintvec_minmax(&ctl_entry, write, buffer, lenp, ppos);
282 if (rc < 0 || !write)
283 return rc;
284 mutex_lock(&smp_cpu_state_mutex);
285 if (hd_set_hiperdispatch_mode(hiperdispatch))
286 topology_schedule_update();
287 mutex_unlock(&smp_cpu_state_mutex);
288 return 0;
289}
290
291static const struct ctl_table hiperdispatch_ctl_table[] = {
292 {
293 .procname = "hiperdispatch",
294 .mode = 0644,
295 .proc_handler = hiperdispatch_ctl_handler,
296 },
297};
298
299static ssize_t hd_steal_threshold_show(struct device *dev,
300 struct device_attribute *attr,
301 char *buf)
302{
303 return sysfs_emit(buf, "%u\n", hd_steal_threshold);
304}
305
306static ssize_t hd_steal_threshold_store(struct device *dev,
307 struct device_attribute *attr,
308 const char *buf,
309 size_t count)
310{
311 unsigned int val;
312 int rc;
313
314 rc = kstrtouint(buf, 0, &val);
315 if (rc)
316 return rc;
317 if (val > 100)
318 return -ERANGE;
319 hd_steal_threshold = val;
320 return count;
321}
322
323static DEVICE_ATTR_RW(hd_steal_threshold);
324
325static ssize_t hd_delay_factor_show(struct device *dev,
326 struct device_attribute *attr,
327 char *buf)
328{
329 return sysfs_emit(buf, "%u\n", hd_delay_factor);
330}
331
332static ssize_t hd_delay_factor_store(struct device *dev,
333 struct device_attribute *attr,
334 const char *buf,
335 size_t count)
336{
337 unsigned int val;
338 int rc;
339
340 rc = kstrtouint(buf, 0, &val);
341 if (rc)
342 return rc;
343 if (!val)
344 return -ERANGE;
345 hd_delay_factor = val;
346 return count;
347}
348
349static DEVICE_ATTR_RW(hd_delay_factor);
350
351static struct attribute *hd_attrs[] = {
352 &dev_attr_hd_steal_threshold.attr,
353 &dev_attr_hd_delay_factor.attr,
354 NULL,
355};
356
357static const struct attribute_group hd_attr_group = {
358 .name = "hiperdispatch",
359 .attrs = hd_attrs,
360};
361
362static int hd_greedy_time_get(void *unused, u64 *val)
363{
364 mutex_lock(&hd_counter_mutex);
365 hd_update_times();
366 *val = hd_high_time;
367 mutex_unlock(&hd_counter_mutex);
368 return 0;
369}
370
371DEFINE_SIMPLE_ATTRIBUTE(hd_greedy_time_fops, hd_greedy_time_get, NULL, "%llu\n");
372
373static int hd_conservative_time_get(void *unused, u64 *val)
374{
375 mutex_lock(&hd_counter_mutex);
376 hd_update_times();
377 *val = hd_low_time;
378 mutex_unlock(&hd_counter_mutex);
379 return 0;
380}
381
382DEFINE_SIMPLE_ATTRIBUTE(hd_conservative_time_fops, hd_conservative_time_get, NULL, "%llu\n");
383
384static int hd_adjustment_count_get(void *unused, u64 *val)
385{
386 *val = atomic64_read(&hd_adjustments);
387 return 0;
388}
389
390DEFINE_SIMPLE_ATTRIBUTE(hd_adjustments_fops, hd_adjustment_count_get, NULL, "%llu\n");
391
392static void __init hd_create_debugfs_counters(void)
393{
394 struct dentry *dir;
395
396 dir = debugfs_create_dir("hiperdispatch", arch_debugfs_dir);
397 debugfs_create_file("conservative_time_ms", 0400, dir, NULL, &hd_conservative_time_fops);
398 debugfs_create_file("greedy_time_ms", 0400, dir, NULL, &hd_greedy_time_fops);
399 debugfs_create_file("adjustment_count", 0400, dir, NULL, &hd_adjustments_fops);
400}
401
402static void __init hd_create_attributes(void)
403{
404 struct device *dev;
405
406 dev = bus_get_dev_root(&cpu_subsys);
407 if (!dev)
408 return;
409 if (sysfs_create_group(&dev->kobj, &hd_attr_group))
410 pr_warn("Unable to create hiperdispatch attribute group\n");
411 put_device(dev);
412}
413
414static int __init hd_init(void)
415{
416 if (IS_ENABLED(CONFIG_HIPERDISPATCH_ON)) {
417 hd_set_hiperdispatch_mode(1);
418 topology_schedule_update();
419 }
420 if (!register_sysctl("s390", hiperdispatch_ctl_table))
421 pr_warn("Failed to register s390.hiperdispatch sysctl attribute\n");
422 hd_create_debugfs_counters();
423 hd_create_attributes();
424 return 0;
425}
426late_initcall(hd_init);