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Subject[PATCH v3 07/10] libperf: Add support for user space counter access
Date
x86 and arm64 can both support direct access of event counters in
userspace. The access sequence is less than trivial and currently exists
in perf test code (tools/perf/arch/x86/tests/rdpmc.c) with copies in
projects such as PAPI and libpfm4.

In order to support usersapce access, an event must be mmapped first
with perf_evsel__mmap(). Then subsequent calls to perf_evsel__read()
will use the fast path (assuming the arch supports it).

Signed-off-by: Rob Herring <robh@kernel.org>
---
v3:
- Split out perf_evsel__mmap() to separate patch
---
tools/lib/perf/evsel.c | 3 +
tools/lib/perf/include/internal/mmap.h | 3 +
tools/lib/perf/mmap.c | 90 ++++++++++++++++++++++++++
tools/lib/perf/tests/test-evsel.c | 63 ++++++++++++++++++
4 files changed, 159 insertions(+)

diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
index 99fa53dc0887..4164e6524453 100644
--- a/tools/lib/perf/evsel.c
+++ b/tools/lib/perf/evsel.c
@@ -222,6 +222,9 @@ int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
if (FD(evsel, cpu, thread) < 0)
return -EINVAL;

+ if (evsel->mmap && !perf_mmap__read_self(evsel->mmap, count))
+ return 0;
+
if (readn(FD(evsel, cpu, thread), count->values, size) <= 0)
return -errno;

diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h
index be7556e0a2b2..5e3422f40ed5 100644
--- a/tools/lib/perf/include/internal/mmap.h
+++ b/tools/lib/perf/include/internal/mmap.h
@@ -11,6 +11,7 @@
#define PERF_SAMPLE_MAX_SIZE (1 << 16)

struct perf_mmap;
+struct perf_counts_values;

typedef void (*libperf_unmap_cb_t)(struct perf_mmap *map);

@@ -52,4 +53,6 @@ void perf_mmap__put(struct perf_mmap *map);

u64 perf_mmap__read_head(struct perf_mmap *map);

+int perf_mmap__read_self(struct perf_mmap *map, struct perf_counts_values *count);
+
#endif /* __LIBPERF_INTERNAL_MMAP_H */
diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
index 79d5ed6c38cc..cb07969cfdbf 100644
--- a/tools/lib/perf/mmap.c
+++ b/tools/lib/perf/mmap.c
@@ -8,9 +8,11 @@
#include <linux/perf_event.h>
#include <perf/mmap.h>
#include <perf/event.h>
+#include <perf/evsel.h>
#include <internal/mmap.h>
#include <internal/lib.h>
#include <linux/kernel.h>
+#include <linux/math64.h>
#include "internal.h"

void perf_mmap__init(struct perf_mmap *map, struct perf_mmap *prev,
@@ -273,3 +275,91 @@ union perf_event *perf_mmap__read_event(struct perf_mmap *map)

return event;
}
+
+#if defined(__i386__) || defined(__x86_64__)
+static u64 read_perf_counter(unsigned int counter)
+{
+ unsigned int low, high;
+
+ asm volatile("rdpmc" : "=a" (low), "=d" (high) : "c" (counter));
+
+ return low | ((u64)high) << 32;
+}
+
+static u64 read_timestamp(void)
+{
+ unsigned int low, high;
+
+ asm volatile("rdtsc" : "=a" (low), "=d" (high));
+
+ return low | ((u64)high) << 32;
+}
+#else
+static u64 read_perf_counter(unsigned int counter) { return 0; }
+static u64 read_timestamp(void) { return 0; }
+#endif
+
+int perf_mmap__read_self(struct perf_mmap *map, struct perf_counts_values *count)
+{
+ struct perf_event_mmap_page *pc = map->base;
+ u32 seq, idx, time_mult = 0, time_shift = 0;
+ u64 cnt, cyc = 0, time_offset = 0, time_cycles = 0, time_mask = ~0ULL;
+
+ BUG_ON(!pc);
+
+ if (!pc->cap_user_rdpmc)
+ return -1;
+
+ do {
+ seq = READ_ONCE(pc->lock);
+ barrier();
+
+ count->ena = READ_ONCE(pc->time_enabled);
+ count->run = READ_ONCE(pc->time_running);
+
+ if (pc->cap_user_time && count->ena != count->run) {
+ cyc = read_timestamp();
+ time_mult = READ_ONCE(pc->time_mult);
+ time_shift = READ_ONCE(pc->time_shift);
+ time_offset = READ_ONCE(pc->time_offset);
+
+ if (pc->cap_user_time_short) {
+ time_cycles = READ_ONCE(pc->time_cycles);
+ time_mask = READ_ONCE(pc->time_mask);
+ }
+ }
+
+ idx = READ_ONCE(pc->index);
+ cnt = READ_ONCE(pc->offset);
+ if (pc->cap_user_rdpmc && idx) {
+ u64 evcnt = read_perf_counter(idx - 1);
+ u16 width = READ_ONCE(pc->pmc_width);
+
+ evcnt <<= 64 - width;
+ evcnt >>= 64 - width;
+ cnt += evcnt;
+ } else
+ return -1;
+
+ barrier();
+ } while (READ_ONCE(pc->lock) != seq);
+
+ if (count->ena != count->run) {
+ u64 delta;
+
+ /* Adjust for cap_usr_time_short, a nop if not */
+ cyc = time_cycles + ((cyc - time_cycles) & time_mask);
+
+ delta = time_offset + mul_u64_u32_shr(cyc, time_mult, time_shift);
+
+ count->ena += delta;
+ if (idx)
+ count->run += delta;
+
+ cnt = mul_u64_u64_div64(cnt, count->ena, count->run);
+ }
+
+ count->val = cnt;
+
+ return 0;
+}
diff --git a/tools/lib/perf/tests/test-evsel.c b/tools/lib/perf/tests/test-evsel.c
index 135722ac965b..a88c12a95e92 100644
--- a/tools/lib/perf/tests/test-evsel.c
+++ b/tools/lib/perf/tests/test-evsel.c
@@ -120,6 +120,67 @@ static int test_stat_thread_enable(void)
return 0;
}

+static int test_stat_user_read(int event)
+{
+ struct perf_counts_values counts = { .val = 0 };
+ struct perf_thread_map *threads;
+ struct perf_evsel *evsel;
+ struct perf_event_mmap_page *pc;
+ struct perf_event_attr attr = {
+ .type = PERF_TYPE_HARDWARE,
+ .config = event,
+ };
+ int err, i;
+
+ threads = perf_thread_map__new_dummy();
+ __T("failed to create threads", threads);
+
+ perf_thread_map__set_pid(threads, 0, 0);
+
+ evsel = perf_evsel__new(&attr);
+ __T("failed to create evsel", evsel);
+
+ err = perf_evsel__open(evsel, NULL, threads);
+ __T("failed to open evsel", err == 0);
+
+ pc = perf_evsel__mmap(evsel, 0x1000);
+ __T("failed to mmap evsel", pc);
+
+#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__)
+ __T("userspace counter access not supported", pc->cap_user_rdpmc);
+ __T("userspace counter access not enabled", pc->index);
+ __T("userspace counter width not set", pc->pmc_width >= 32);
+#endif
+
+ perf_evsel__read(evsel, 0, 0, &counts);
+ __T("failed to read value for evsel", counts.val != 0);
+
+ for (i = 0; i < 5; i++) {
+ volatile int count = 0x10000 << i;
+ __u64 start, end, last = 0;
+
+ __T_VERBOSE("\tloop = %u, ", count);
+
+ perf_evsel__read(evsel, 0, 0, &counts);
+ start = counts.val;
+
+ while (count--) ;
+
+ perf_evsel__read(evsel, 0, 0, &counts);
+ end = counts.val;
+
+ __T("invalid counter data", (end - start) > last);
+ last = end - start;
+ __T_VERBOSE("count = %llu\n", end - start);
+ }
+
+ perf_evsel__close(evsel);
+ perf_evsel__delete(evsel);
+
+ perf_thread_map__put(threads);
+ return 0;
+}
+
int main(int argc, char **argv)
{
__T_START;
@@ -129,6 +190,8 @@ int main(int argc, char **argv)
test_stat_cpu();
test_stat_thread();
test_stat_thread_enable();
+ test_stat_user_read(PERF_COUNT_HW_INSTRUCTIONS);
+ test_stat_user_read(PERF_COUNT_HW_CPU_CYCLES);

__T_END;
return 0;
--
2.25.1
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