Re: [PATCH v2 05/10] riscv: Prepare for user-space perf event mmap support

From: Atish Patra
Date: Tue Jun 20 2023 - 11:28:01 EST

On Fri, Jun 16, 2023 at 1:57 AM Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> wrote:
>
> On Fri, Jun 16, 2023 at 10:28 AM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote:
> >
> > On Fri, May 12, 2023 at 1:58 AM Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> > > ---
> > > 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.
>
> Yes, this is done in patch 7 when I adapt the perf SBI backend to
> allow the user access.
>

Yes. I missed that earlier. Thanks.

> >
> > > + 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



--
Regards,
Atish