vpa-dtl.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * Perf interface to expose Dispatch Trace Log counters.
  4 *
  5 * Copyright (C) 2024 Kajol Jain, IBM Corporation
  6 */
  7
  8#ifdef CONFIG_PPC_SPLPAR
  9#define pr_fmt(fmt) "vpa_dtl: " fmt
 10
 11#include <asm/dtl.h>
 12#include <linux/perf_event.h>
 13#include <asm/plpar_wrappers.h>
 14#include <linux/vmalloc.h>
 15
 16#define EVENT(_name, _code)     enum{_name = _code}
 17
 18/*
 19 * Based on Power Architecture Platform Reference(PAPR) documentation,
 20 * Table 14.14. Per Virtual Processor Area, below Dispatch Trace Log(DTL)
 21 * Enable Mask used to get corresponding virtual processor dispatch
 22 * to preempt traces:
 23 *   DTL_CEDE(0x1): Trace voluntary (OS initiated) virtual
 24 *   processor waits
 25 *   DTL_PREEMPT(0x2): Trace time slice preempts
 26 *   DTL_FAULT(0x4): Trace virtual partition memory page
 27 faults.
 28 *   DTL_ALL(0x7): Trace all (DTL_CEDE | DTL_PREEMPT | DTL_FAULT)
 29 *
 30 * Event codes based on Dispatch Trace Log Enable Mask.
 31 */
 32EVENT(DTL_CEDE,         0x1);
 33EVENT(DTL_PREEMPT,      0x2);
 34EVENT(DTL_FAULT,        0x4);
 35EVENT(DTL_ALL,          0x7);
 36
 37GENERIC_EVENT_ATTR(dtl_cede, DTL_CEDE);
 38GENERIC_EVENT_ATTR(dtl_preempt, DTL_PREEMPT);
 39GENERIC_EVENT_ATTR(dtl_fault, DTL_FAULT);
 40GENERIC_EVENT_ATTR(dtl_all, DTL_ALL);
 41
 42PMU_FORMAT_ATTR(event, "config:0-7");
 43
 44static struct attribute *events_attr[] = {
 45	GENERIC_EVENT_PTR(DTL_CEDE),
 46	GENERIC_EVENT_PTR(DTL_PREEMPT),
 47	GENERIC_EVENT_PTR(DTL_FAULT),
 48	GENERIC_EVENT_PTR(DTL_ALL),
 49	NULL
 50};
 51
 52static struct attribute_group event_group = {
 53	.name = "events",
 54	.attrs = events_attr,
 55};
 56
 57static struct attribute *format_attrs[] = {
 58	&format_attr_event.attr,
 59	NULL,
 60};
 61
 62static const struct attribute_group format_group = {
 63	.name = "format",
 64	.attrs = format_attrs,
 65};
 66
 67static const struct attribute_group *attr_groups[] = {
 68	&format_group,
 69	&event_group,
 70	NULL,
 71};
 72
 73struct vpa_dtl {
 74	struct dtl_entry	*buf;
 75	u64			last_idx;
 76};
 77
 78struct vpa_pmu_ctx {
 79	struct perf_output_handle handle;
 80};
 81
 82struct vpa_pmu_buf {
 83	int     nr_pages;
 84	bool    snapshot;
 85	u64     *base;
 86	u64     size;
 87	u64     head;
 88	u64	head_size;
 89	/* boot timebase and frequency needs to be saved only at once */
 90	int	boottb_freq_saved;
 91	u64	threshold;
 92	bool	full;
 93};
 94
 95/*
 96 * To corelate each DTL entry with other events across CPU's,
 97 * we need to map timebase from "struct dtl_entry" which phyp
 98 * provides with boot timebase. This also needs timebase frequency.
 99 * Formula is: ((timbase from DTL entry - boot time) / frequency)
100 *
101 * To match with size of "struct dtl_entry" to ease post processing,
102 * padded 24 bytes to the structure.
103 */
104struct boottb_freq {
105	u64	boot_tb;
106	u64	tb_freq;
107	u64	timebase;
108	u64	padded[3];
109};
110
111static DEFINE_PER_CPU(struct vpa_pmu_ctx, vpa_pmu_ctx);
112static DEFINE_PER_CPU(struct vpa_dtl, vpa_dtl_cpu);
113
114/* variable to capture reference count for the active dtl threads */
115static int dtl_global_refc;
116static spinlock_t dtl_global_lock = __SPIN_LOCK_UNLOCKED(dtl_global_lock);
117
118/*
119 * Capture DTL data in AUX buffer
120 */
121static void vpa_dtl_capture_aux(long *n_entries, struct vpa_pmu_buf *buf,
122		struct vpa_dtl *dtl, int index)
123{
124	struct dtl_entry *aux_copy_buf = (struct dtl_entry *)buf->base;
125
126	/*
127	 * check if there is enough space to contain the
128	 * DTL data. If not, save the data for available
129	 * memory and set full to true.
130	 */
131	if (buf->head + *n_entries >= buf->threshold) {
132		*n_entries = buf->threshold - buf->head;
133		buf->full = 1;
134	}
135
136	/*
137	 * Copy to AUX buffer from per-thread address
138	 */
139	memcpy(aux_copy_buf + buf->head, &dtl->buf[index], *n_entries * sizeof(struct dtl_entry));
140
141	if (buf->full) {
142		/*
143		 * Set head of private aux to zero when buffer is full
144		 * so that next data will be copied to beginning of the
145		 * buffer
146		 */
147		buf->head = 0;
148		return;
149	}
150
151	buf->head += *n_entries;
152
153	return;
154}
155
156/*
157 * Function to dump the dispatch trace log buffer data to the
158 * perf data.
159 *
160 * perf_aux_output_begin: This function is called before writing
161 * to AUX area. This returns the pointer to aux area private structure,
162 * ie "struct vpa_pmu_buf" here which is set in setup_aux() function.
163 * The function obtains the output handle (used in perf_aux_output_end).
164 * when capture completes in vpa_dtl_capture_aux(), call perf_aux_output_end()
165 * to commit the recorded data.
166 *
167 * perf_aux_output_end: This function commits data by adjusting the
168 * aux_head of "struct perf_buffer". aux_tail will be moved in perf tools
169 * side when writing the data from aux buffer to perf.data file in disk.
170 *
171 * Here in the private aux structure, we maintain head to know where
172 * to copy data next time in the PMU driver. vpa_pmu_buf->head is moved to
173 * maintain the aux head for PMU driver. It is responsiblity of PMU
174 * driver to make sure data is copied between perf_aux_output_begin and
175 * perf_aux_output_end.
176 *
177 * After data is copied in vpa_dtl_capture_aux() function, perf_aux_output_end()
178 * is called to move the aux->head of "struct perf_buffer" to indicate size of
179 * data in aux buffer. This will post a PERF_RECORD_AUX into the perf buffer.
180 * Data will be written to disk only when the allocated buffer is full.
181 *
182 * By this approach, all the DTL data will be present as-is in the
183 * perf.data. The data will be pre-processed in perf tools side when doing
184 * perf report/perf script and this will avoid time taken to create samples
185 * in the kernel space.
186 */
187static void vpa_dtl_dump_sample_data(struct perf_event *event)
188{
189	u64 cur_idx, last_idx, i;
190	u64 boot_tb;
191	struct boottb_freq boottb_freq;
192
193	/* actual number of entries read */
194	long n_read = 0, read_size = 0;
195
196	/* number of entries added to dtl buffer */
197	long n_req;
198
199	struct vpa_pmu_ctx *vpa_ctx = this_cpu_ptr(&vpa_pmu_ctx);
200
201	struct vpa_pmu_buf *aux_buf;
202
203	struct vpa_dtl *dtl = &per_cpu(vpa_dtl_cpu, event->cpu);
204	u64 size;
205
206	cur_idx = be64_to_cpu(lppaca_of(event->cpu).dtl_idx);
207	last_idx = dtl->last_idx;
208
209	if (last_idx + N_DISPATCH_LOG <= cur_idx)
210		last_idx = cur_idx - N_DISPATCH_LOG + 1;
211
212	n_req = cur_idx - last_idx;
213
214	/* no new entry added to the buffer, return */
215	if (n_req <= 0)
216		return;
217
218	dtl->last_idx = last_idx + n_req;
219	boot_tb = get_boot_tb();
220
221	i = last_idx % N_DISPATCH_LOG;
222
223	aux_buf = perf_aux_output_begin(&vpa_ctx->handle, event);
224	if (!aux_buf) {
225		pr_debug("returning. no aux\n");
226		return;
227	}
228
229	if (!aux_buf->boottb_freq_saved) {
230		pr_debug("Copying boot tb to aux buffer: %lld\n", boot_tb);
231		/* Save boot_tb to convert raw timebase to it's relative system boot time */
232		boottb_freq.boot_tb = boot_tb;
233		/* Save tb_ticks_per_sec to convert timebase to sec */
234		boottb_freq.tb_freq = tb_ticks_per_sec;
235		boottb_freq.timebase = 0;
236		memcpy(aux_buf->base, &boottb_freq, sizeof(boottb_freq));
237		aux_buf->head += 1;
238		aux_buf->boottb_freq_saved = 1;
239		n_read += 1;
240	}
241
242	/* read the tail of the buffer if we've wrapped */
243	if (i + n_req > N_DISPATCH_LOG) {
244		read_size = N_DISPATCH_LOG - i;
245		vpa_dtl_capture_aux(&read_size, aux_buf, dtl, i);
246		n_req -= read_size;
247		n_read += read_size;
248		i = 0;
249		if (aux_buf->full) {
250			size = (n_read * sizeof(struct dtl_entry));
251			if ((size +  aux_buf->head_size) > aux_buf->size) {
252				size = aux_buf->size - aux_buf->head_size;
253				perf_aux_output_end(&vpa_ctx->handle, size);
254				aux_buf->head = 0;
255				aux_buf->head_size = 0;
256			} else {
257				aux_buf->head_size += (n_read * sizeof(struct dtl_entry));
258				perf_aux_output_end(&vpa_ctx->handle, n_read * sizeof(struct dtl_entry));
259			}
260			goto out;
261		}
262	}
263
264	/* .. and now the head */
265	vpa_dtl_capture_aux(&n_req, aux_buf, dtl, i);
266
267	size = ((n_req + n_read) * sizeof(struct dtl_entry));
268	if ((size +  aux_buf->head_size) > aux_buf->size) {
269		size = aux_buf->size - aux_buf->head_size;
270		perf_aux_output_end(&vpa_ctx->handle, size);
271		aux_buf->head = 0;
272		aux_buf->head_size = 0;
273	} else {
274		aux_buf->head_size += ((n_req + n_read) * sizeof(struct dtl_entry));
275		/* Move the aux->head to indicate size of data in aux buffer */
276		perf_aux_output_end(&vpa_ctx->handle, (n_req + n_read) * sizeof(struct dtl_entry));
277	}
278out:
279	aux_buf->full = 0;
280}
281
282/*
283 * The VPA Dispatch Trace log counters do not interrupt on overflow.
284 * Therefore, the kernel needs to poll the counters to avoid missing
285 * an overflow using hrtimer. The timer interval is based on sample_period
286 * count provided by user, and minimum interval is 1 millisecond.
287 */
288static enum hrtimer_restart vpa_dtl_hrtimer_handle(struct hrtimer *hrtimer)
289{
290	struct perf_event *event;
291	u64 period;
292
293	event = container_of(hrtimer, struct perf_event, hw.hrtimer);
294
295	if (event->state != PERF_EVENT_STATE_ACTIVE)
296		return HRTIMER_NORESTART;
297
298	vpa_dtl_dump_sample_data(event);
299	period = max_t(u64, NSEC_PER_MSEC, event->hw.sample_period);
300	hrtimer_forward_now(hrtimer, ns_to_ktime(period));
301
302	return HRTIMER_RESTART;
303}
304
305static void vpa_dtl_start_hrtimer(struct perf_event *event)
306{
307	u64 period;
308	struct hw_perf_event *hwc = &event->hw;
309
310	period = max_t(u64, NSEC_PER_MSEC, hwc->sample_period);
311	hrtimer_start(&hwc->hrtimer, ns_to_ktime(period), HRTIMER_MODE_REL_PINNED);
312}
313
314static void vpa_dtl_stop_hrtimer(struct perf_event *event)
315{
316	struct hw_perf_event *hwc = &event->hw;
317
318	hrtimer_cancel(&hwc->hrtimer);
319}
320
321static void vpa_dtl_reset_global_refc(struct perf_event *event)
322{
323	spin_lock(&dtl_global_lock);
324	dtl_global_refc--;
325	if (dtl_global_refc <= 0) {
326		dtl_global_refc = 0;
327		up_write(&dtl_access_lock);
328	}
329	spin_unlock(&dtl_global_lock);
330}
331
332static int vpa_dtl_mem_alloc(int cpu)
333{
334	struct vpa_dtl *dtl = &per_cpu(vpa_dtl_cpu, cpu);
335	struct dtl_entry *buf = NULL;
336
337	/* Check for dispatch trace log buffer cache */
338	if (!dtl_cache)
339		return -ENOMEM;
340
341	buf = kmem_cache_alloc_node(dtl_cache, GFP_KERNEL | GFP_ATOMIC, cpu_to_node(cpu));
342	if (!buf) {
343		pr_warn("buffer allocation failed for cpu %d\n", cpu);
344		return -ENOMEM;
345	}
346	dtl->buf = buf;
347	return 0;
348}
349
350static int vpa_dtl_event_init(struct perf_event *event)
351{
352	struct hw_perf_event *hwc = &event->hw;
353
354	/* test the event attr type for PMU enumeration */
355	if (event->attr.type != event->pmu->type)
356		return -ENOENT;
357
358	if (!perfmon_capable())
359		return -EACCES;
360
361	/* Return if this is a counting event */
362	if (!is_sampling_event(event))
363		return -EOPNOTSUPP;
364
365	/* no branch sampling */
366	if (has_branch_stack(event))
367		return -EOPNOTSUPP;
368
369	/* Invalid eventcode */
370	switch (event->attr.config) {
371	case DTL_LOG_CEDE:
372	case DTL_LOG_PREEMPT:
373	case DTL_LOG_FAULT:
374	case DTL_LOG_ALL:
375		break;
376	default:
377		return -EINVAL;
378	}
379
380	spin_lock(&dtl_global_lock);
381
382	/*
383	 * To ensure there are no other conflicting dtl users
384	 * (example: /proc/powerpc/vcpudispatch_stats or debugfs dtl),
385	 * below code try to take the dtl_access_lock.
386	 * The dtl_access_lock is a rwlock defined in dtl.h, which is used
387	 * to unsure there is no conflicting dtl users.
388	 * Based on below code, vpa_dtl pmu tries to take write access lock
389	 * and also checks for dtl_global_refc, to make sure that the
390	 * dtl_access_lock is taken by vpa_dtl pmu interface.
391	 */
392	if (dtl_global_refc == 0 && !down_write_trylock(&dtl_access_lock)) {
393		spin_unlock(&dtl_global_lock);
394		return -EBUSY;
395	}
396
397	/* Allocate dtl buffer memory */
398	if (vpa_dtl_mem_alloc(event->cpu)) {
399		spin_unlock(&dtl_global_lock);
400		return -ENOMEM;
401	}
402
403	/*
404	 * Increment the number of active vpa_dtl pmu threads. The
405	 * dtl_global_refc is used to keep count of cpu threads that
406	 * currently capturing dtl data using vpa_dtl pmu interface.
407	 */
408	dtl_global_refc++;
409
410	spin_unlock(&dtl_global_lock);
411
412	hrtimer_setup(&hwc->hrtimer, vpa_dtl_hrtimer_handle, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
413
414	/*
415	 * Since hrtimers have a fixed rate, we can do a static freq->period
416	 * mapping and avoid the whole period adjust feedback stuff.
417	 */
418	if (event->attr.freq) {
419		long freq = event->attr.sample_freq;
420
421		event->attr.sample_period = NSEC_PER_SEC / freq;
422		hwc->sample_period = event->attr.sample_period;
423		local64_set(&hwc->period_left, hwc->sample_period);
424		hwc->last_period = hwc->sample_period;
425		event->attr.freq = 0;
426	}
427
428	event->destroy = vpa_dtl_reset_global_refc;
429	return 0;
430}
431
432static int vpa_dtl_event_add(struct perf_event *event, int flags)
433{
434	int ret, hwcpu;
435	unsigned long addr;
436	struct vpa_dtl *dtl = &per_cpu(vpa_dtl_cpu, event->cpu);
437
438	/*
439	 * Register our dtl buffer with the hypervisor. The
440	 * HV expects the buffer size to be passed in the second
441	 * word of the buffer. Refer section '14.11.3.2. H_REGISTER_VPA'
442	 * from PAPR for more information.
443	 */
444	((u32 *)dtl->buf)[1] = cpu_to_be32(DISPATCH_LOG_BYTES);
445	dtl->last_idx = 0;
446
447	hwcpu = get_hard_smp_processor_id(event->cpu);
448	addr = __pa(dtl->buf);
449
450	ret = register_dtl(hwcpu, addr);
451	if (ret) {
452		pr_warn("DTL registration for cpu %d (hw %d) failed with %d\n",
453			event->cpu, hwcpu, ret);
454		return ret;
455	}
456
457	/* set our initial buffer indices */
458	lppaca_of(event->cpu).dtl_idx = 0;
459
460	/*
461	 * Ensure that our updates to the lppaca fields have
462	 * occurred before we actually enable the logging
463	 */
464	smp_wmb();
465
466	/* enable event logging */
467	lppaca_of(event->cpu).dtl_enable_mask = event->attr.config;
468
469	vpa_dtl_start_hrtimer(event);
470
471	return 0;
472}
473
474static void vpa_dtl_event_del(struct perf_event *event, int flags)
475{
476	int hwcpu = get_hard_smp_processor_id(event->cpu);
477	struct vpa_dtl *dtl = &per_cpu(vpa_dtl_cpu, event->cpu);
478
479	vpa_dtl_stop_hrtimer(event);
480	unregister_dtl(hwcpu);
481	kmem_cache_free(dtl_cache, dtl->buf);
482	dtl->buf = NULL;
483	lppaca_of(event->cpu).dtl_enable_mask = 0x0;
484}
485
486/*
487 * This function definition is empty as vpa_dtl_dump_sample_data
488 * is used to parse and dump the dispatch trace log data,
489 * to perf data.
490 */
491static void vpa_dtl_event_read(struct perf_event *event)
492{
493}
494
495/*
496 * Set up pmu-private data structures for an AUX area
497 * **pages contains the aux buffer allocated for this event
498 * for the corresponding cpu. rb_alloc_aux uses "alloc_pages_node"
499 * and returns pointer to each page address. Map these pages to
500 * contiguous space using vmap and use that as base address.
501 *
502 * The aux private data structure ie, "struct vpa_pmu_buf" mainly
503 * saves
504 * - buf->base: aux buffer base address
505 * - buf->head: offset from base address where data will be written to.
506 * - buf->size: Size of allocated memory
507 */
508static void *vpa_dtl_setup_aux(struct perf_event *event, void **pages,
509		int nr_pages, bool snapshot)
510{
511	int i, cpu = event->cpu;
512	struct vpa_pmu_buf *buf __free(kfree) = NULL;
513	struct page **pglist __free(kfree) = NULL;
514
515	/* We need at least one page for this to work. */
516	if (!nr_pages)
517		return NULL;
518
519	if (cpu == -1)
520		cpu = raw_smp_processor_id();
521
522	buf = kzalloc_node(sizeof(*buf), GFP_KERNEL, cpu_to_node(cpu));
523	if (!buf)
524		return NULL;
525
526	pglist = kcalloc(nr_pages, sizeof(*pglist), GFP_KERNEL);
527	if (!pglist)
528		return NULL;
529
530	for (i = 0; i < nr_pages; ++i)
531		pglist[i] = virt_to_page(pages[i]);
532
533	buf->base = vmap(pglist, nr_pages, VM_MAP, PAGE_KERNEL);
534	if (!buf->base)
535		return NULL;
536
537	buf->nr_pages = nr_pages;
538	buf->snapshot = false;
539
540	buf->size = nr_pages << PAGE_SHIFT;
541	buf->head = 0;
542	buf->head_size = 0;
543	buf->boottb_freq_saved = 0;
544	buf->threshold = ((buf->size - 32) / sizeof(struct dtl_entry));
545	return no_free_ptr(buf);
546}
547
548/*
549 * free pmu-private AUX data structures
550 */
551static void vpa_dtl_free_aux(void *aux)
552{
553	struct vpa_pmu_buf *buf = aux;
554
555	vunmap(buf->base);
556	kfree(buf);
557}
558
559static struct pmu vpa_dtl_pmu = {
560	.task_ctx_nr = perf_invalid_context,
561
562	.name = "vpa_dtl",
563	.attr_groups = attr_groups,
564	.event_init  = vpa_dtl_event_init,
565	.add         = vpa_dtl_event_add,
566	.del         = vpa_dtl_event_del,
567	.read        = vpa_dtl_event_read,
568	.setup_aux   = vpa_dtl_setup_aux,
569	.free_aux    = vpa_dtl_free_aux,
570	.capabilities = PERF_PMU_CAP_NO_EXCLUDE | PERF_PMU_CAP_EXCLUSIVE,
571};
572
573static int vpa_dtl_init(void)
574{
575	int r;
576
577	if (!firmware_has_feature(FW_FEATURE_SPLPAR)) {
578		pr_debug("not a shared virtualized system, not enabling\n");
579		return -ENODEV;
580	}
581
582	/* This driver is intended only for L1 host. */
583	if (is_kvm_guest()) {
584		pr_debug("Only supported for L1 host system\n");
585		return -ENODEV;
586	}
587
588	r = perf_pmu_register(&vpa_dtl_pmu, vpa_dtl_pmu.name, -1);
589	if (r)
590		return r;
591
592	return 0;
593}
594
595device_initcall(vpa_dtl_init);
596#endif //CONFIG_PPC_SPLPAR