[PATCH v4 05/10] riscv: Prepare for user-space perf event mmap support

Alexandre Ghiti
2023-07-27T14:22:17Z

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@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
---
drivers/perf/riscv_pmu.c | 105 +++++++++++++++++++++++++++++++++
include/linux/perf/riscv_pmu.h | 4 ++
2 files changed, 109 insertions(+)

diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
index ebca5eab9c9b..432ad2e80ce3 100644
--- a/drivers/perf/riscv_pmu.c
+++ b/drivers/perf/riscv_pmu.c
@@ -14,9 +14,73 @@
#include <linux/perf/riscv_pmu.h>
#include <linux/printk.h>
#include <linux/smp.h>
+#include <linux/sched_clock.h>

#include <asm/sbi.h>

+static bool riscv_perf_user_access(struct perf_event *event)
+{
+ return ((event->attr.type == PERF_TYPE_HARDWARE) ||
+ (event->attr.type == PERF_TYPE_HW_CACHE) ||
+ (event->attr.type == PERF_TYPE_RAW)) &&
+ !!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT);
+}
+
+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 = riscv_perf_user_access(event);
+
+ userpg->pmc_width = 64;
+
+ 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;
+}
+
static unsigned long csr_read_num(int csr_num)
{
#define switchcase_csr_read(__csr_num, __val) {\
@@ -171,6 +235,8 @@ 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 +333,9 @@ 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 +352,39 @@ 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 +409,9 @@ 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 5deeea0be7cb..43282e22ebe1 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;
--
2.39.2