Messages in this thread | | | From | Rob Herring <> | Date | Tue, 4 May 2021 21:12:19 -0500 | Subject | Re: [PATCH v6 06/10] libperf: Add support for user space counter access |
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On Tue, May 4, 2021 at 4:41 PM Ian Rogers <irogers@google.com> wrote: > > 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.
IMO, we should just delete that version. One less slightly wrong version...
> > + } > > + > > + 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/
I don't think so because if we don't have a valid counter index, we exit before this if.
> > > + } > > + > > + 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.
I suppose we can just exit if open fails on this test.
Rob
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