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Message-ID: <CAOnJCUL8t-BMfLX0uvjbFK9TFVyqEdCnkYN9aE0hB4NXEtRHZw@mail.gmail.com>
Date: Fri, 16 Jun 2023 01:28:09 -0700
From: Atish Patra <atishp@...shpatra.org>
To: Alexandre Ghiti <alexghiti@...osinc.com>
Cc: Jonathan Corbet <corbet@....net>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Anup Patel <anup@...infault.org>,
Will Deacon <will@...nel.org>, Rob Herring <robh@...nel.org>,
Andrew Jones <ajones@...tanamicro.com>,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org, linux-riscv@...ts.infradead.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 05/10] riscv: Prepare for user-space perf event mmap support
On Fri, May 12, 2023 at 1:58 AM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
>
> Provide all the necessary bits in the generic riscv pmu driver to be
> able to mmap perf events in userspace: the heavy lifting lies in the
> driver backend, namely the legacy and sbi implementations.
>
> Note that arch_perf_update_userpage is almost a copy of arm64 code.
>
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> ---
> arch/riscv/kernel/Makefile | 2 +-
> arch/riscv/kernel/perf_event.c | 58 ++++++++++++++++++++++++++++++++++
> drivers/perf/riscv_pmu.c | 41 ++++++++++++++++++++++++
> include/linux/perf/riscv_pmu.h | 4 +++
> 4 files changed, 104 insertions(+), 1 deletion(-)
> create mode 100644 arch/riscv/kernel/perf_event.c
>
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index 4cf303a779ab..0d215fd9860d 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -70,7 +70,7 @@ obj-$(CONFIG_DYNAMIC_FTRACE) += mcount-dyn.o
>
> obj-$(CONFIG_TRACE_IRQFLAGS) += trace_irq.o
>
> -obj-$(CONFIG_PERF_EVENTS) += perf_callchain.o
> +obj-$(CONFIG_PERF_EVENTS) += perf_callchain.o perf_event.o
> obj-$(CONFIG_HAVE_PERF_REGS) += perf_regs.o
> obj-$(CONFIG_RISCV_SBI) += sbi.o
> ifeq ($(CONFIG_RISCV_SBI), y)
> diff --git a/arch/riscv/kernel/perf_event.c b/arch/riscv/kernel/perf_event.c
> new file mode 100644
> index 000000000000..94174a0fc251
> --- /dev/null
> +++ b/arch/riscv/kernel/perf_event.c
> @@ -0,0 +1,58 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <linux/sched_clock.h>
> +
> +void arch_perf_update_userpage(struct perf_event *event,
> + struct perf_event_mmap_page *userpg, u64 now)
> +{
> + struct clock_read_data *rd;
> + unsigned int seq;
> + u64 ns;
> +
> + userpg->cap_user_time = 0;
> + userpg->cap_user_time_zero = 0;
> + userpg->cap_user_time_short = 0;
> + userpg->cap_user_rdpmc =
> + !!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT);
> +
> + userpg->pmc_width = 64;
> +
The counter width is 64 for cycle & instret. Other hpmcounter can have
different width.
This information should retrieved from counter info.
> + do {
> + rd = sched_clock_read_begin(&seq);
> +
> + userpg->time_mult = rd->mult;
> + userpg->time_shift = rd->shift;
> + userpg->time_zero = rd->epoch_ns;
> + userpg->time_cycles = rd->epoch_cyc;
> + userpg->time_mask = rd->sched_clock_mask;
> +
> + /*
> + * Subtract the cycle base, such that software that
> + * doesn't know about cap_user_time_short still 'works'
> + * assuming no wraps.
> + */
> + ns = mul_u64_u32_shr(rd->epoch_cyc, rd->mult, rd->shift);
> + userpg->time_zero -= ns;
> +
> + } while (sched_clock_read_retry(seq));
> +
> + userpg->time_offset = userpg->time_zero - now;
> +
> + /*
> + * time_shift is not expected to be greater than 31 due to
> + * the original published conversion algorithm shifting a
> + * 32-bit value (now specifies a 64-bit value) - refer
> + * perf_event_mmap_page documentation in perf_event.h.
> + */
> + if (userpg->time_shift == 32) {
> + userpg->time_shift = 31;
> + userpg->time_mult >>= 1;
> + }
> +
> + /*
> + * Internal timekeeping for enabled/running/stopped times
> + * is always computed with the sched_clock.
> + */
> + userpg->cap_user_time = 1;
> + userpg->cap_user_time_zero = 1;
> + userpg->cap_user_time_short = 1;
> +}
> diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
> index ebca5eab9c9b..af69da268246 100644
> --- a/drivers/perf/riscv_pmu.c
> +++ b/drivers/perf/riscv_pmu.c
> @@ -171,6 +171,8 @@ int riscv_pmu_event_set_period(struct perf_event *event)
>
> local64_set(&hwc->prev_count, (u64)-left);
>
> + perf_event_update_userpage(event);
> +
> return overflow;
> }
>
> @@ -267,6 +269,9 @@ static int riscv_pmu_event_init(struct perf_event *event)
> hwc->idx = -1;
> hwc->event_base = mapped_event;
>
> + if (rvpmu->event_init)
> + rvpmu->event_init(event);
> +
> if (!is_sampling_event(event)) {
> /*
> * For non-sampling runs, limit the sample_period to half
> @@ -283,6 +288,39 @@ static int riscv_pmu_event_init(struct perf_event *event)
> return 0;
> }
>
> +static int riscv_pmu_event_idx(struct perf_event *event)
> +{
> + struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
> +
> + if (!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT))
> + return 0;
> +
> + if (rvpmu->csr_index)
> + return rvpmu->csr_index(event) + 1;
> +
> + return 0;
> +}
> +
> +static void riscv_pmu_event_mapped(struct perf_event *event, struct mm_struct *mm)
> +{
> + struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
> +
> + if (rvpmu->event_mapped) {
> + rvpmu->event_mapped(event, mm);
> + perf_event_update_userpage(event);
> + }
> +}
> +
> +static void riscv_pmu_event_unmapped(struct perf_event *event, struct mm_struct *mm)
> +{
> + struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
> +
> + if (rvpmu->event_unmapped) {
> + rvpmu->event_unmapped(event, mm);
> + perf_event_update_userpage(event);
> + }
> +}
> +
> struct riscv_pmu *riscv_pmu_alloc(void)
> {
> struct riscv_pmu *pmu;
> @@ -307,6 +345,9 @@ struct riscv_pmu *riscv_pmu_alloc(void)
> }
> pmu->pmu = (struct pmu) {
> .event_init = riscv_pmu_event_init,
> + .event_mapped = riscv_pmu_event_mapped,
> + .event_unmapped = riscv_pmu_event_unmapped,
> + .event_idx = riscv_pmu_event_idx,
> .add = riscv_pmu_add,
> .del = riscv_pmu_del,
> .start = riscv_pmu_start,
> diff --git a/include/linux/perf/riscv_pmu.h b/include/linux/perf/riscv_pmu.h
> index 9f70d94942e0..1452c8af3b67 100644
> --- a/include/linux/perf/riscv_pmu.h
> +++ b/include/linux/perf/riscv_pmu.h
> @@ -55,6 +55,10 @@ struct riscv_pmu {
> void (*ctr_start)(struct perf_event *event, u64 init_val);
> void (*ctr_stop)(struct perf_event *event, unsigned long flag);
> int (*event_map)(struct perf_event *event, u64 *config);
> + void (*event_init)(struct perf_event *event);
> + void (*event_mapped)(struct perf_event *event, struct mm_struct *mm);
> + void (*event_unmapped)(struct perf_event *event, struct mm_struct *mm);
> + uint8_t (*csr_index)(struct perf_event *event);
>
> struct cpu_hw_events __percpu *hw_events;
> struct hlist_node node;
> --
> 2.37.2
>
--
Regards,
Atish
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