RE: [EXT] Re: [PATCH v11 1/4] lib: add generic support for reading PMU events

[Tomasz Duszynski <tduszynski@marvell.com>]

>-----Original Message-----
>From: Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>
>Sent: Friday, February 17, 2023 12:51 AM
>To: dev@dpdk.org
>Subject: [EXT] Re: [PATCH v11 1/4] lib: add generic support for reading PMU events
>
>External Email
>
>----------------------------------------------------------------------
>16/02/2023 17:54, Tomasz Duszynski пишет:
>> Add support for programming PMU counters and reading their values in
>> runtime bypassing kernel completely.
>>
>> This is especially useful in cases where CPU cores are isolated i.e
>> run dedicated tasks. In such cases one cannot use standard perf
>> utility without sacrificing latency and performance.
>>
>> Signed-off-by: Tomasz Duszynski <tduszynski@marvell.com>
>> Acked-by: Morten Brørup <mb@smartsharesystems.com>
>> ---
>>   MAINTAINERS                            |   5 +
>>   app/test/meson.build                   |   2 +
>>   app/test/test_pmu.c                    |  62 ++++
>>   doc/api/doxy-api-index.md              |   3 +-
>>   doc/api/doxy-api.conf.in               |   1 +
>>   doc/guides/prog_guide/profile_app.rst  |  12 +
>>   doc/guides/rel_notes/release_23_03.rst |   7 +
>>   lib/meson.build                        |   1 +
>>   lib/pmu/meson.build                    |  13 +
>>   lib/pmu/pmu_private.h                  |  32 ++
>>   lib/pmu/rte_pmu.c                      | 460 +++++++++++++++++++++++++
>>   lib/pmu/rte_pmu.h                      | 212 ++++++++++++
>>   lib/pmu/version.map                    |  15 +
>>   13 files changed, 824 insertions(+), 1 deletion(-)
>>   create mode 100644 app/test/test_pmu.c
>>   create mode 100644 lib/pmu/meson.build
>>   create mode 100644 lib/pmu/pmu_private.h
>>   create mode 100644 lib/pmu/rte_pmu.c
>>   create mode 100644 lib/pmu/rte_pmu.h
>>   create mode 100644 lib/pmu/version.map
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS index 3495946d0f..d37f242120
>> 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -1697,6 +1697,11 @@ M: Nithin Dabilpuram <ndabilpuram@marvell.com>
>>   M: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>   F: lib/node/
>>
>> +PMU - EXPERIMENTAL
>> +M: Tomasz Duszynski <tduszynski@marvell.com>
>> +F: lib/pmu/
>> +F: app/test/test_pmu*
>> +
>>
>>   Test Applications
>>   -----------------
>> diff --git a/app/test/meson.build b/app/test/meson.build index
>> f34d19e3c3..6b61b7fc32 100644
>> --- a/app/test/meson.build
>> +++ b/app/test/meson.build
>> @@ -111,6 +111,7 @@ test_sources = files(
>>           'test_reciprocal_division_perf.c',
>>           'test_red.c',
>>           'test_pie.c',
>> +        'test_pmu.c',
>>           'test_reorder.c',
>>           'test_rib.c',
>>           'test_rib6.c',
>> @@ -239,6 +240,7 @@ fast_tests = [
>>           ['kni_autotest', false, true],
>>           ['kvargs_autotest', true, true],
>>           ['member_autotest', true, true],
>> +        ['pmu_autotest', true, true],
>>           ['power_cpufreq_autotest', false, true],
>>           ['power_autotest', true, true],
>>           ['power_kvm_vm_autotest', false, true], diff --git
>> a/app/test/test_pmu.c b/app/test/test_pmu.c new file mode 100644 index
>> 0000000000..c257638e8b
>> --- /dev/null
>> +++ b/app/test/test_pmu.c
>> @@ -0,0 +1,62 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause
>> + * Copyright(C) 2023 Marvell International Ltd.
>> + */
>> +
>> +#include "test.h"
>> +
>> +#ifndef RTE_EXEC_ENV_LINUX
>> +
>> +static int
>> +test_pmu(void)
>> +{
>> +	printf("pmu_autotest only supported on Linux, skipping test\n");
>> +	return TEST_SKIPPED;
>> +}
>> +
>> +#else
>> +
>> +#include <rte_pmu.h>
>> +
>> +static int
>> +test_pmu_read(void)
>> +{
>> +	const char *name = NULL;
>> +	int tries = 10, event;
>> +	uint64_t val = 0;
>> +
>> +	if (name == NULL) {
>> +		printf("PMU not supported on this arch\n");
>> +		return TEST_SKIPPED;
>> +	}
>> +
>> +	if (rte_pmu_init() < 0)
>> +		return TEST_SKIPPED;
>> +
>> +	event = rte_pmu_add_event(name);
>> +	while (tries--)
>> +		val += rte_pmu_read(event);
>> +
>> +	rte_pmu_fini();
>> +
>> +	return val ? TEST_SUCCESS : TEST_FAILED; }
>> +
>> +static struct unit_test_suite pmu_tests = {
>> +	.suite_name = "pmu autotest",
>> +	.setup = NULL,
>> +	.teardown = NULL,
>> +	.unit_test_cases = {
>> +		TEST_CASE(test_pmu_read),
>> +		TEST_CASES_END()
>> +	}
>> +};
>> +
>> +static int
>> +test_pmu(void)
>> +{
>> +	return unit_test_suite_runner(&pmu_tests);
>> +}
>> +
>> +#endif /* RTE_EXEC_ENV_LINUX */
>> +
>> +REGISTER_TEST_COMMAND(pmu_autotest, test_pmu);
>> diff --git a/doc/api/doxy-api-index.md b/doc/api/doxy-api-index.md
>> index 2deec7ea19..a8e04a195d 100644
>> --- a/doc/api/doxy-api-index.md
>> +++ b/doc/api/doxy-api-index.md
>> @@ -223,7 +223,8 @@ The public API headers are grouped by topics:
>>     [log](@ref rte_log.h),
>>     [errno](@ref rte_errno.h),
>>     [trace](@ref rte_trace.h),
>> -  [trace_point](@ref rte_trace_point.h)
>> +  [trace_point](@ref rte_trace_point.h),  [pmu](@ref rte_pmu.h)
>>
>>   - **misc**:
>>     [EAL config](@ref rte_eal.h),
>> diff --git a/doc/api/doxy-api.conf.in b/doc/api/doxy-api.conf.in index
>> e859426099..350b5a8c94 100644
>> --- a/doc/api/doxy-api.conf.in
>> +++ b/doc/api/doxy-api.conf.in
>> @@ -63,6 +63,7 @@ INPUT                   = @TOPDIR@/doc/api/doxy-api-index.md \
>>                             @TOPDIR@/lib/pci \
>>                             @TOPDIR@/lib/pdump \
>>                             @TOPDIR@/lib/pipeline \
>> +                          @TOPDIR@/lib/pmu \
>>                             @TOPDIR@/lib/port \
>>                             @TOPDIR@/lib/power \
>>                             @TOPDIR@/lib/rawdev \ diff --git
>> a/doc/guides/prog_guide/profile_app.rst
>> b/doc/guides/prog_guide/profile_app.rst
>> index 14292d4c25..89e38cd301 100644
>> --- a/doc/guides/prog_guide/profile_app.rst
>> +++ b/doc/guides/prog_guide/profile_app.rst
>> @@ -7,6 +7,18 @@ Profile Your Application
>>   The following sections describe methods of profiling DPDK applications on
>>   different architectures.
>>
>> +Performance counter based profiling
>> +-----------------------------------
>> +
>> +Majority of architectures support some performance monitoring unit (PMU).
>> +Such unit provides programmable counters that monitor specific events.
>> +
>> +Different tools gather that information, like for example perf.
>> +However, in some scenarios when CPU cores are isolated and run
>> +dedicated tasks interrupting those tasks with perf may be undesirable.
>> +
>> +In such cases, an application can use the PMU library to read such events via
>``rte_pmu_read()``.
>> +
>>
>>   Profiling on x86
>>   ----------------
>> diff --git a/doc/guides/rel_notes/release_23_03.rst
>> b/doc/guides/rel_notes/release_23_03.rst
>> index ab998a5357..20622efe58 100644
>> --- a/doc/guides/rel_notes/release_23_03.rst
>> +++ b/doc/guides/rel_notes/release_23_03.rst
>> @@ -147,6 +147,13 @@ New Features
>>     * Added support to capture packets at each graph node with packet metadata and
>>       node name.
>>
>> +* **Added PMU library.**
>> +
>> +  Added a new performance monitoring unit (PMU) library which allows
>> + applications  to perform self monitoring activities without depending on external utilities
>like perf.
>> +  After integration with :doc:`../prog_guide/trace_lib` data gathered
>> + from hardware counters  can be stored in CTF format for further analysis.
>> +
>>
>>   Removed Items
>>   -------------
>> diff --git a/lib/meson.build b/lib/meson.build index
>> 450c061d2b..8a42d45d20 100644
>> --- a/lib/meson.build
>> +++ b/lib/meson.build
>> @@ -11,6 +11,7 @@
>>   libraries = [
>>           'kvargs', # eal depends on kvargs
>>           'telemetry', # basic info querying
>> +        'pmu',
>>           'eal', # everything depends on eal
>>           'ring',
>>           'rcu', # rcu depends on ring diff --git
>> a/lib/pmu/meson.build b/lib/pmu/meson.build new file mode 100644 index
>> 0000000000..a4160b494e
>> --- /dev/null
>> +++ b/lib/pmu/meson.build
>> @@ -0,0 +1,13 @@
>> +# SPDX-License-Identifier: BSD-3-Clause # Copyright(C) 2023 Marvell
>> +International Ltd.
>> +
>> +if not is_linux
>> +    build = false
>> +    reason = 'only supported on Linux'
>> +    subdir_done()
>> +endif
>> +
>> +includes = [global_inc]
>> +
>> +sources = files('rte_pmu.c')
>> +headers = files('rte_pmu.h')
>> diff --git a/lib/pmu/pmu_private.h b/lib/pmu/pmu_private.h new file
>> mode 100644 index 0000000000..b9f8c1ddc8
>> --- /dev/null
>> +++ b/lib/pmu/pmu_private.h
>> @@ -0,0 +1,32 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause
>> + * Copyright(c) 2023 Marvell
>> + */
>> +
>> +#ifndef _PMU_PRIVATE_H_
>> +#define _PMU_PRIVATE_H_
>> +
>> +/**
>> + * Architecture specific PMU init callback.
>> + *
>> + * @return
>> + *   0 in case of success, negative value otherwise.
>> + */
>> +int
>> +pmu_arch_init(void);
>> +
>> +/**
>> + * Architecture specific PMU cleanup callback.
>> + */
>> +void
>> +pmu_arch_fini(void);
>> +
>> +/**
>> + * Apply architecture specific settings to config before passing it to syscall.
>> + *
>> + * @param config
>> + *   Architecture specific event configuration. Consult kernel sources for available options.
>> + */
>> +void
>> +pmu_arch_fixup_config(uint64_t config[3]);
>> +
>> +#endif /* _PMU_PRIVATE_H_ */
>> diff --git a/lib/pmu/rte_pmu.c b/lib/pmu/rte_pmu.c new file mode
>> 100644 index 0000000000..950f999cb7
>> --- /dev/null
>> +++ b/lib/pmu/rte_pmu.c
>> @@ -0,0 +1,460 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause
>> + * Copyright(C) 2023 Marvell International Ltd.
>> + */
>> +
>> +#include <ctype.h>
>> +#include <dirent.h>
>> +#include <errno.h>
>> +#include <regex.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +#include <sys/ioctl.h>
>> +#include <sys/mman.h>
>> +#include <sys/queue.h>
>> +#include <sys/syscall.h>
>> +#include <unistd.h>
>> +
>> +#include <rte_atomic.h>
>> +#include <rte_per_lcore.h>
>> +#include <rte_pmu.h>
>> +#include <rte_spinlock.h>
>> +#include <rte_tailq.h>
>> +
>> +#include "pmu_private.h"
>> +
>> +#define EVENT_SOURCE_DEVICES_PATH "/sys/bus/event_source/devices"
>
>
>I suppose that pass (as the whole implementation) is linux specific?
>If so, wouldn't it make sense to have it under linux subdir?
>

There are not any plans to support that elsewhere currently so flat
directory structure is good enough. 

>> +
>> +#define GENMASK_ULL(h, l) ((~0ULL - (1ULL << (l)) + 1) & (~0ULL >>
>> +((64 - 1 - (h))))) #define FIELD_PREP(m, v) (((uint64_t)(v) <<
>> +(__builtin_ffsll(m) - 1)) & (m))
>> +
>> +RTE_DEFINE_PER_LCORE(struct rte_pmu_event_group, _event_group);
>> +struct rte_pmu rte_pmu;
>
>Do we really need struct declaration here?
>

What’s the problem with this placement precisely?

>
>> +/*
>> + * Following __rte_weak functions provide default no-op.
>> +Architectures should override them if
>> + * necessary.
>> + */
>> +
>> +int
>> +__rte_weak pmu_arch_init(void)
>> +{
>> +	return 0;
>> +}
>> +
>> +void
>> +__rte_weak pmu_arch_fini(void)
>> +{
>> +}
>> +
>> +void
>> +__rte_weak pmu_arch_fixup_config(uint64_t __rte_unused config[3]) { }
>> +
>> +static int
>> +get_term_format(const char *name, int *num, uint64_t *mask) {
>> +	char path[PATH_MAX];
>> +	char *config = NULL;
>> +	int high, low, ret;
>> +	FILE *fp;
>> +
>> +	*num = *mask = 0;
>> +	snprintf(path, sizeof(path), EVENT_SOURCE_DEVICES_PATH "/%s/format/%s", rte_pmu.name, name);
>> +	fp = fopen(path, "r");
>> +	if (fp == NULL)
>> +		return -errno;
>> +
>> +	errno = 0;
>> +	ret = fscanf(fp, "%m[^:]:%d-%d", &config, &low, &high);
>> +	if (ret < 2) {
>> +		ret = -ENODATA;
>> +		goto out;
>> +	}
>> +	if (errno) {
>> +		ret = -errno;
>> +		goto out;
>> +	}
>> +
>> +	if (ret == 2)
>> +		high = low;
>> +
>> +	*mask = GENMASK_ULL(high, low);
>> +	/* Last digit should be [012]. If last digit is missing 0 is implied. */
>> +	*num = config[strlen(config) - 1];
>> +	*num = isdigit(*num) ? *num - '0' : 0;
>> +
>> +	ret = 0;
>> +out:
>> +	free(config);
>> +	fclose(fp);
>> +
>> +	return ret;
>> +}
>> +
>> +static int
>> +parse_event(char *buf, uint64_t config[3]) {
>> +	char *token, *term;
>> +	int num, ret, val;
>> +	uint64_t mask;
>> +
>> +	config[0] = config[1] = config[2] = 0;
>> +
>> +	token = strtok(buf, ",");
>> +	while (token) {
>> +		errno = 0;
>> +		/* <term>=<value> */
>> +		ret = sscanf(token, "%m[^=]=%i", &term, &val);
>> +		if (ret < 1)
>> +			return -ENODATA;
>> +		if (errno)
>> +			return -errno;
>> +		if (ret == 1)
>> +			val = 1;
>> +
>> +		ret = get_term_format(term, &num, &mask);
>> +		free(term);
>> +		if (ret)
>> +			return ret;
>> +
>> +		config[num] |= FIELD_PREP(mask, val);
>> +		token = strtok(NULL, ",");
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int
>> +get_event_config(const char *name, uint64_t config[3]) {
>> +	char path[PATH_MAX], buf[BUFSIZ];
>> +	FILE *fp;
>> +	int ret;
>> +
>> +	snprintf(path, sizeof(path), EVENT_SOURCE_DEVICES_PATH "/%s/events/%s", rte_pmu.name, name);
>> +	fp = fopen(path, "r");
>> +	if (fp == NULL)
>> +		return -errno;
>> +
>> +	ret = fread(buf, 1, sizeof(buf), fp);
>> +	if (ret == 0) {
>> +		fclose(fp);
>> +
>> +		return -EINVAL;
>> +	}
>> +	fclose(fp);
>> +	buf[ret] = '\0';
>> +
>> +	return parse_event(buf, config);
>> +}
>> +
>> +static int
>> +do_perf_event_open(uint64_t config[3], int group_fd) {
>> +	struct perf_event_attr attr = {
>> +		.size = sizeof(struct perf_event_attr),
>> +		.type = PERF_TYPE_RAW,
>> +		.exclude_kernel = 1,
>> +		.exclude_hv = 1,
>> +		.disabled = 1,
>> +	};
>> +
>> +	pmu_arch_fixup_config(config);
>> +
>> +	attr.config = config[0];
>> +	attr.config1 = config[1];
>> +	attr.config2 = config[2];
>> +
>> +	return syscall(SYS_perf_event_open, &attr, 0, -1, group_fd, 0); }
>> +
>> +static int
>> +open_events(struct rte_pmu_event_group *group) {
>> +	struct rte_pmu_event *event;
>> +	uint64_t config[3];
>> +	int num = 0, ret;
>> +
>> +	/* group leader gets created first, with fd = -1 */
>> +	group->fds[0] = -1;
>> +
>> +	TAILQ_FOREACH(event, &rte_pmu.event_list, next) {
>> +		ret = get_event_config(event->name, config);
>> +		if (ret)
>> +			continue;
>> +
>> +		ret = do_perf_event_open(config, group->fds[0]);
>> +		if (ret == -1) {
>> +			ret = -errno;
>> +			goto out;
>> +		}
>> +
>> +		group->fds[event->index] = ret;
>> +		num++;
>> +	}
>> +
>> +	return 0;
>> +out:
>> +	for (--num; num >= 0; num--) {
>> +		close(group->fds[num]);
>> +		group->fds[num] = -1;
>> +	}
>> +
>> +
>> +	return ret;
>> +}
>> +
>> +static int
>> +mmap_events(struct rte_pmu_event_group *group) {
>> +	long page_size = sysconf(_SC_PAGE_SIZE);
>> +	unsigned int i;
>> +	void *addr;
>> +	int ret;
>> +
>> +	for (i = 0; i < rte_pmu.num_group_events; i++) {
>> +		addr = mmap(0, page_size, PROT_READ, MAP_SHARED, group->fds[i], 0);
>> +		if (addr == MAP_FAILED) {
>> +			ret = -errno;
>> +			goto out;
>> +		}
>> +
>> +		group->mmap_pages[i] = addr;
>> +		if (!group->mmap_pages[i]->cap_user_rdpmc) {
>> +			ret = -EPERM;
>> +			goto out;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +out:
>> +	for (; i; i--) {
>> +		munmap(group->mmap_pages[i - 1], page_size);
>> +		group->mmap_pages[i - 1] = NULL;
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +static void
>> +cleanup_events(struct rte_pmu_event_group *group) {
>> +	unsigned int i;
>> +
>> +	if (group->fds[0] != -1)
>> +		ioctl(group->fds[0], PERF_EVENT_IOC_DISABLE, PERF_IOC_FLAG_GROUP);
>> +
>> +	for (i = 0; i < rte_pmu.num_group_events; i++) {
>> +		if (group->mmap_pages[i]) {
>> +			munmap(group->mmap_pages[i], sysconf(_SC_PAGE_SIZE));
>> +			group->mmap_pages[i] = NULL;
>> +		}
>> +
>> +		if (group->fds[i] != -1) {
>> +			close(group->fds[i]);
>> +			group->fds[i] = -1;
>> +		}
>> +	}
>> +
>> +	group->enabled = false;
>> +}
>> +
>> +int
>> +__rte_pmu_enable_group(void)
>> +{
>> +	struct rte_pmu_event_group *group = &RTE_PER_LCORE(_event_group);
>> +	int ret;
>> +
>> +	if (rte_pmu.num_group_events == 0)
>> +		return -ENODEV;
>> +
>> +	ret = open_events(group);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = mmap_events(group);
>> +	if (ret)
>> +		goto out;
>> +
>> +	if (ioctl(group->fds[0], PERF_EVENT_IOC_RESET, PERF_IOC_FLAG_GROUP) == -1) {
>> +		ret = -errno;
>> +		goto out;
>> +	}
>> +
>> +	if (ioctl(group->fds[0], PERF_EVENT_IOC_ENABLE, PERF_IOC_FLAG_GROUP) == -1) {
>> +		ret = -errno;
>> +		goto out;
>> +	}
>> +
>> +	rte_spinlock_lock(&rte_pmu.lock);
>> +	TAILQ_INSERT_TAIL(&rte_pmu.event_group_list, group, next);
>> +	rte_spinlock_unlock(&rte_pmu.lock);
>> +	group->enabled = true;
>> +
>> +	return 0;
>> +
>> +out:
>> +	cleanup_events(group);
>> +
>> +	return ret;
>> +}
>> +
>> +static int
>> +scan_pmus(void)
>> +{
>> +	char path[PATH_MAX];
>> +	struct dirent *dent;
>> +	const char *name;
>> +	DIR *dirp;
>> +
>> +	dirp = opendir(EVENT_SOURCE_DEVICES_PATH);
>> +	if (dirp == NULL)
>> +		return -errno;
>> +
>> +	while ((dent = readdir(dirp))) {
>> +		name = dent->d_name;
>> +		if (name[0] == '.')
>> +			continue;
>> +
>> +		/* sysfs entry should either contain cpus or be a cpu */
>> +		if (!strcmp(name, "cpu"))
>> +			break;
>> +
>> +		snprintf(path, sizeof(path), EVENT_SOURCE_DEVICES_PATH "/%s/cpus", name);
>> +		if (access(path, F_OK) == 0)
>> +			break;
>> +	}
>> +
>> +	if (dent) {
>> +		rte_pmu.name = strdup(name);
>> +		if (rte_pmu.name == NULL) {
>> +			closedir(dirp);
>> +
>> +			return -ENOMEM;
>> +		}
>> +	}
>> +
>> +	closedir(dirp);
>> +
>> +	return rte_pmu.name ? 0 : -ENODEV;
>> +}
>> +
>> +static struct rte_pmu_event *
>> +new_event(const char *name)
>> +{
>> +	struct rte_pmu_event *event;
>> +
>> +	event = calloc(1, sizeof(*event));
>> +	if (event == NULL)
>> +		goto out;
>> +
>> +	event->name = strdup(name);
>> +	if (event->name == NULL) {
>> +		free(event);
>> +		event = NULL;
>> +	}
>> +
>> +out:
>> +	return event;
>> +}
>> +
>> +static void
>> +free_event(struct rte_pmu_event *event) {
>> +	free(event->name);
>> +	free(event);
>> +}
>> +
>> +int
>> +rte_pmu_add_event(const char *name)
>> +{
>> +	struct rte_pmu_event *event;
>> +	char path[PATH_MAX];
>> +
>> +	if (rte_pmu.name == NULL)
>> +		return -ENODEV;
>> +
>> +	if (rte_pmu.num_group_events + 1 >= MAX_NUM_GROUP_EVENTS)
>> +		return -ENOSPC;
>> +
>> +	snprintf(path, sizeof(path), EVENT_SOURCE_DEVICES_PATH "/%s/events/%s", rte_pmu.name, name);
>> +	if (access(path, R_OK))
>> +		return -ENODEV;
>> +
>> +	TAILQ_FOREACH(event, &rte_pmu.event_list, next) {
>> +		if (!strcmp(event->name, name))
>> +			return event->index;
>> +		continue;
>> +	}
>> +
>> +	event = new_event(name);
>> +	if (event == NULL)
>> +		return -ENOMEM;
>> +
>> +	event->index = rte_pmu.num_group_events++;
>> +	TAILQ_INSERT_TAIL(&rte_pmu.event_list, event, next);
>> +
>> +	return event->index;
>> +}
>> +
>> +int
>> +rte_pmu_init(void)
>> +{
>> +	int ret;
>> +
>> +	/* Allow calling init from multiple contexts within a single thread. This simplifies
>> +	 * resource management a bit e.g in case fast-path tracepoint has already been enabled
>> +	 * via command line but application doesn't care enough and performs init/fini again.
>> +	 */
>> +	if (rte_pmu.initialized != 0) {
>> +		rte_pmu.initialized++;
>> +		return 0;
>> +	}
>> +
>> +	ret = scan_pmus();
>> +	if (ret)
>> +		goto out;
>> +
>> +	ret = pmu_arch_init();
>> +	if (ret)
>> +		goto out;
>> +
>> +	TAILQ_INIT(&rte_pmu.event_list);
>> +	TAILQ_INIT(&rte_pmu.event_group_list);
>> +	rte_spinlock_init(&rte_pmu.lock);
>> +	rte_pmu.initialized = 1;
>> +
>> +	return 0;
>> +out:
>> +	free(rte_pmu.name);
>> +	rte_pmu.name = NULL;
>> +
>> +	return ret;
>> +}
>> +
>> +void
>> +rte_pmu_fini(void)
>> +{
>> +	struct rte_pmu_event_group *group, *tmp_group;
>> +	struct rte_pmu_event *event, *tmp_event;
>> +
>> +	/* cleanup once init count drops to zero */
>> +	if (rte_pmu.initialized == 0 || --rte_pmu.initialized != 0)
>> +		return;
>> +
>> +	RTE_TAILQ_FOREACH_SAFE(event, &rte_pmu.event_list, next, tmp_event) {
>> +		TAILQ_REMOVE(&rte_pmu.event_list, event, next);
>> +		free_event(event);
>> +	}
>> +
>> +	RTE_TAILQ_FOREACH_SAFE(group, &rte_pmu.event_group_list, next, tmp_group) {
>> +		TAILQ_REMOVE(&rte_pmu.event_group_list, group, next);
>> +		cleanup_events(group);
>> +	}
>> +
>> +	pmu_arch_fini();
>> +	free(rte_pmu.name);
>> +	rte_pmu.name = NULL;
>> +	rte_pmu.num_group_events = 0;
>> +}
>> diff --git a/lib/pmu/rte_pmu.h b/lib/pmu/rte_pmu.h new file mode
>> 100644 index 0000000000..6b664c3336
>> --- /dev/null
>> +++ b/lib/pmu/rte_pmu.h
>> @@ -0,0 +1,212 @@
>> +/* SPDX-License-Identifier: BSD-3-Clause
>> + * Copyright(c) 2023 Marvell
>> + */
>> +
>> +#ifndef _RTE_PMU_H_
>> +#define _RTE_PMU_H_
>> +
>> +/**
>> + * @file
>> + *
>> + * PMU event tracing operations
>> + *
>> + * This file defines generic API and types necessary to setup PMU and
>> + * read selected counters in runtime.
>> + */
>> +
>> +#ifdef __cplusplus
>> +extern "C" {
>> +#endif
>> +
>> +#include <linux/perf_event.h>
>> +
>> +#include <rte_atomic.h>
>> +#include <rte_branch_prediction.h>
>> +#include <rte_common.h>
>> +#include <rte_compat.h>
>> +#include <rte_spinlock.h>
>> +
>> +/** Maximum number of events in a group */ #define
>> +MAX_NUM_GROUP_EVENTS 8
>> +
>> +/**
>> + * A structure describing a group of events.
>> + */
>> +struct rte_pmu_event_group {
>> +	struct perf_event_mmap_page *mmap_pages[MAX_NUM_GROUP_EVENTS]; /**< array of user pages */
>> +	int fds[MAX_NUM_GROUP_EVENTS]; /**< array of event descriptors */
>> +	bool enabled; /**< true if group was enabled on particular lcore */
>> +	TAILQ_ENTRY(rte_pmu_event_group) next; /**< list entry */ }
>> +__rte_cache_aligned;
>> +
>> +/**
>> + * A structure describing an event.
>> + */
>> +struct rte_pmu_event {
>> +	char *name; /**< name of an event */
>> +	unsigned int index; /**< event index into fds/mmap_pages */
>> +	TAILQ_ENTRY(rte_pmu_event) next; /**< list entry */ };
>> +
>> +/**
>> + * A PMU state container.
>> + */
>> +struct rte_pmu {
>> +	char *name; /**< name of core PMU listed under /sys/bus/event_source/devices */
>> +	rte_spinlock_t lock; /**< serialize access to event group list */
>> +	TAILQ_HEAD(, rte_pmu_event_group) event_group_list; /**< list of event groups */
>> +	unsigned int num_group_events; /**< number of events in a group */
>> +	TAILQ_HEAD(, rte_pmu_event) event_list; /**< list of matching events */
>> +	unsigned int initialized; /**< initialization counter */ };
>> +
>> +/** lcore event group */
>> +RTE_DECLARE_PER_LCORE(struct rte_pmu_event_group, _event_group);
>> +
>> +/** PMU state container */
>> +extern struct rte_pmu rte_pmu;
>> +
>> +/** Each architecture supporting PMU needs to provide its own version
>> +*/ #ifndef rte_pmu_pmc_read #define rte_pmu_pmc_read(index) ({ 0; })
>> +#endif
>> +
>> +/**
>> + * @warning
>> + * @b EXPERIMENTAL: this API may change without prior notice
>> + *
>> + * Read PMU counter.
>> + *
>> + * @warning This should be not called directly.
>> + *
>> + * @param pc
>> + *   Pointer to the mmapped user page.
>> + * @return
>> + *   Counter value read from hardware.
>> + */
>> +static __rte_always_inline uint64_t
>> +__rte_pmu_read_userpage(struct perf_event_mmap_page *pc) {
>> +	uint64_t width, offset;
>> +	uint32_t seq, index;
>> +	int64_t pmc;
>> +
>> +	for (;;) {
>> +		seq = pc->lock;
>> +		rte_compiler_barrier();
>
>Are you sure that compiler_barrier() is enough here?
>On some archs CPU itself has freedom to re-order reads.
>Or I am missing something obvious here?
>

It's a matter of not keeping old stuff cached in registers 
and making sure that we have two reads of lock. CPU reordering
won't do any harm here. 

>> +		index = pc->index;
>> +		offset = pc->offset;
>> +		width = pc->pmc_width;
>> +
>> +		/* index set to 0 means that particular counter cannot be used */
>> +		if (likely(pc->cap_user_rdpmc && index)) {
>> +			pmc = rte_pmu_pmc_read(index - 1);
>> +			pmc <<= 64 - width;
>> +			pmc >>= 64 - width;
>> +			offset += pmc;
>> +		}
>> +
>> +		rte_compiler_barrier();
>> +
>> +		if (likely(pc->lock == seq))
>> +			return offset;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +/**
>> + * @warning
>> + * @b EXPERIMENTAL: this API may change without prior notice
>> + *
>> + * Enable group of events on the calling lcore.
>> + *
>> + * @warning This should be not called directly.
>> + *
>> + * @return
>> + *   0 in case of success, negative value otherwise.
>> + */
>> +__rte_experimental
>> +int
>> +__rte_pmu_enable_group(void);
>> +
>> +/**
>> + * @warning
>> + * @b EXPERIMENTAL: this API may change without prior notice
>> + *
>> + * Initialize PMU library.
>> + *
>> + * @warning This should be not called directly.
>> + *
>> + * @return
>> + *   0 in case of success, negative value otherwise.
>> + */
>> +__rte_experimental
>> +int
>> +rte_pmu_init(void);
>> +
>> +/**
>> + * @warning
>> + * @b EXPERIMENTAL: this API may change without prior notice
>> + *
>> + * Finalize PMU library. This should be called after PMU counters are no longer being read.
>> + */
>> +__rte_experimental
>> +void
>> +rte_pmu_fini(void);
>> +
>> +/**
>> + * @warning
>> + * @b EXPERIMENTAL: this API may change without prior notice
>> + *
>> + * Add event to the group of enabled events.
>> + *
>> + * @param name
>> + *   Name of an event listed under /sys/bus/event_source/devices/pmu/events.
>> + * @return
>> + *   Event index in case of success, negative value otherwise.
>> + */
>> +__rte_experimental
>> +int
>> +rte_pmu_add_event(const char *name);
>> +
>> +/**
>> + * @warning
>> + * @b EXPERIMENTAL: this API may change without prior notice
>> + *
>> + * Read hardware counter configured to count occurrences of an event.
>> + *
>> + * @param index
>> + *   Index of an event to be read.
>> + * @return
>> + *   Event value read from register. In case of errors or lack of support
>> + *   0 is returned. In other words, stream of zeros in a trace file
>> + *   indicates problem with reading particular PMU event register.
>> + */
>> +__rte_experimental
>> +static __rte_always_inline uint64_t
>> +rte_pmu_read(unsigned int index)
>> +{
>> +	struct rte_pmu_event_group *group = &RTE_PER_LCORE(_event_group);
>> +	int ret;
>> +
>> +	if (unlikely(!rte_pmu.initialized))
>> +		return 0;
>> +
>> +	if (unlikely(!group->enabled)) {
>> +		ret = __rte_pmu_enable_group();
>> +		if (ret)
>> +			return 0;
>> +	}
>> +
>> +	if (unlikely(index >= rte_pmu.num_group_events))
>> +		return 0;
>> +
>> +	return __rte_pmu_read_userpage(group->mmap_pages[index]);
>> +}
>> +
>> +#ifdef __cplusplus
>> +}
>> +#endif
>> +
>> +#endif /* _RTE_PMU_H_ */
>> diff --git a/lib/pmu/version.map b/lib/pmu/version.map new file mode
>> 100644 index 0000000000..39a4f279c1
>> --- /dev/null
>> +++ b/lib/pmu/version.map
>> @@ -0,0 +1,15 @@
>> +DPDK_23 {
>> +	local: *;
>> +};
>> +
>> +EXPERIMENTAL {
>> +	global:
>> +
>> +	__rte_pmu_enable_group;
>> +	per_lcore__event_group;
>> +	rte_pmu;
>> +	rte_pmu_add_event;
>> +	rte_pmu_fini;
>> +	rte_pmu_init;
>> +	rte_pmu_read;
>> +};