Messages in this thread | | | From | Ian Rogers <> | Date | Tue, 4 May 2021 14:40:52 -0700 | Subject | Re: [PATCH v6 06/10] libperf: Add support for user space counter access |
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On Wed, Mar 10, 2021 at 4:08 PM Rob Herring <robh@kernel.org> wrote: > > 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> > --- > v6: > - Adapt to mmap changes adding MMAP NULL check > v5: > - Make raw count s64 instead of u64 so that counter width shifting > works > - Adapt to mmap changes > v4: > - Update perf_evsel__mmap size to pages > v3: > - Split out perf_evsel__mmap() to separate patch > --- > tools/lib/perf/evsel.c | 4 ++ > tools/lib/perf/include/internal/mmap.h | 3 + > tools/lib/perf/mmap.c | 88 ++++++++++++++++++++++++++ > tools/lib/perf/tests/test-evsel.c | 65 +++++++++++++++++++ > 4 files changed, 160 insertions(+) > > diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c > index 1057e9b15528..4d67343d36c9 100644 > --- a/tools/lib/perf/evsel.c > +++ b/tools/lib/perf/evsel.c > @@ -242,6 +242,10 @@ int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread, > if (FD(evsel, cpu, thread) < 0) > return -EINVAL; > > + if (MMAP(evsel, cpu, thread) && > + !perf_mmap__read_self(MMAP(evsel, cpu, thread), 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..915469f00cf4 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 +275,89 @@ 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; > + > + if (!pc || !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); > + }
Nit, this is now out of sync with the comment code in perf_event.h.
> + } > + > + idx = READ_ONCE(pc->index); > + cnt = READ_ONCE(pc->offset); > + if (pc->cap_user_rdpmc && idx) { > + s64 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);
Does this still suffer the divide by zero if multiplexing hasn't run the counter? If so, we still need to add something like: https://lore.kernel.org/lkml/CAP-5=fVRdqvswtyQMg5cB+ntTGda+SAYskjTQednEH-AeZo13g@mail.gmail.com/
> + } > + > + count->val = cnt; > + > + return 0; > +} > diff --git a/tools/lib/perf/tests/test-evsel.c b/tools/lib/perf/tests/test-evsel.c > index 0ad82d7a2a51..54fb4809b9ee 100644 > --- a/tools/lib/perf/tests/test-evsel.c > +++ b/tools/lib/perf/tests/test-evsel.c > @@ -120,6 +120,69 @@ 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, > + };
A nit, previously test-evsel was able to run and pass on a hypervisor. As now there is a reliance on hardware events the evsel open fails on a hypervisor. It'd be nice if we could detect running on a hypervisor and test software events in that case.
Thanks, Ian
> + 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); > + > + err = perf_evsel__mmap(evsel, 0); > + __T("failed to mmap evsel", err == 0); > + > + pc = perf_evsel__mmap_base(evsel, 0, 0); > + > +#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 +192,8 @@ 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 tests_failed == 0 ? 0 : -1; > -- > 2.27.0 >
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