[RFC v2 6/7] RISC-V: Add perf platform driver based on SBI PMU extension
Anup Patel
anup at brainfault.org
Tue Jun 1 08:57:50 PDT 2021
On Tue, Jun 1, 2021 at 9:18 PM Anup Patel <anup at brainfault.org> wrote:
>
> On Tue, Jun 1, 2021 at 6:40 PM Stanislaw Kardach <kda at semihalf.com> wrote:
> >
> > On Fri, May 28, 2021 at 11:44:04AM -0700, Atish Patra wrote:
> > > RISC-V SBI specification added a PMU extension that allows to configure
> > > /start/stop any pmu counter. The RISC-V perf can use most of the generic
> > > perf features except interrupt overflow and event filtering based on
> > > privilege mode which will be added in future.
> > >
> > > It also allows to monitor a handful of firmware counters that can provide
> > > insights into firmware activity during a performance analysis.
> > >
> > > Signed-off-by: Atish Patra <atish.patra at wdc.com>
> > > ---
> > > drivers/perf/Kconfig | 8 +
> > > drivers/perf/Makefile | 1 +
> > > drivers/perf/riscv_pmu.c | 2 +
> > > drivers/perf/riscv_pmu_sbi.c | 537 +++++++++++++++++++++++++++++++++++
> > > 4 files changed, 548 insertions(+)
> > > create mode 100644 drivers/perf/riscv_pmu_sbi.c
> > >
> > > diff --git a/drivers/perf/Kconfig b/drivers/perf/Kconfig
> > > index 1546a487d970..2acb5feaab35 100644
> > > --- a/drivers/perf/Kconfig
> > > +++ b/drivers/perf/Kconfig
> > > @@ -73,6 +73,14 @@ config RISCV_PMU_LEGACY
> > > implementation on RISC-V based systems. This only allows counting
> > > of cycle/instruction counter and will be removed in future.
> > >
> > > +config RISCV_PMU_SBI
> > > + depends on RISCV_PMU
> > > + bool "RISC-V PMU based on SBI PMU extension"
> > > + default y
> > > + help
> > > + Say y if you want to use the CPU performance monitor
> > > + using SBI PMU extension on RISC-V based systems.
> > > +
> > > config ARM_PMU_ACPI
> > > depends on ARM_PMU && ACPI
> > > def_bool y
> > > diff --git a/drivers/perf/Makefile b/drivers/perf/Makefile
> > > index e8aa666a9d28..7bcac4b5a983 100644
> > > --- a/drivers/perf/Makefile
> > > +++ b/drivers/perf/Makefile
> > > @@ -13,6 +13,7 @@ obj-$(CONFIG_QCOM_L3_PMU) += qcom_l3_pmu.o
> > > obj-$(CONFIG_RISCV_PMU) += riscv_pmu.o
> > > ifeq ($(CONFIG_RISCV_PMU), y)
> > > obj-$(CONFIG_RISCV_PMU_LEGACY) += riscv_pmu_legacy.o
> > > +obj-$(CONFIG_RISCV_PMU_SBI) += riscv_pmu_sbi.o
> > > endif
> > > obj-$(CONFIG_THUNDERX2_PMU) += thunderx2_pmu.o
> > > obj-$(CONFIG_XGENE_PMU) += xgene_pmu.o
> > > diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
> > > index c184aa50134d..596af3a40948 100644
> > > --- a/drivers/perf/riscv_pmu.c
> > > +++ b/drivers/perf/riscv_pmu.c
> > > @@ -15,6 +15,8 @@
> > > #include <linux/printk.h>
> > > #include <linux/smp.h>
> > >
> > > +#include <asm/sbi.h>
> > > +
> > > static unsigned long csr_read_num(int csr_num)
> > > {
> > > #define switchcase_csr_read(__csr_num, __val) {\
> > > diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> > > new file mode 100644
> > > index 000000000000..80dd1de428c4
> > > --- /dev/null
> > > +++ b/drivers/perf/riscv_pmu_sbi.c
> > > @@ -0,0 +1,537 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * RISC-V performance counter support.
> > > + *
> > > + * Copyright (C) 2021 Western Digital Corporation or its affiliates.
> > > + *
> > > + * This code is based on ARM perf event code which is in turn based on
> > > + * sparc64 and x86 code.
> > > + */
> > > +
> > > +#include <linux/mod_devicetable.h>
> > > +#include <linux/perf/riscv_pmu.h>
> > > +#include <linux/platform_device.h>
> > > +
> > > +#include <asm/sbi.h>
> > > +
> > > +union sbi_pmu_ctr_info {
> > > + unsigned long value;
> > > + struct {
> > > + unsigned long csr:12;
> > > + unsigned long width:6;
> > > +#if __riscv_xlen == 32
> > > + unsigned long reserved:13;
> > > +#else
> > > + unsigned long reserved:45;
> > > +#endif
> > > + unsigned long type:1;
> > > + };
> > > +};
> > > +
> > > +/**
> > > + * RISC-V doesn't have hetergenous harts yet. This need to be part of
> > > + * per_cpu in case of harts with different pmu counters
> > > + */
> > > +static union sbi_pmu_ctr_info *pmu_ctr_list;
> > > +
> > > +struct pmu_event_data {
> > > + union {
> > > + union {
> > > + struct hw_gen_event {
> > > + uint32_t event_code:16;
> > > + uint32_t event_type:4;
> > > + uint32_t reserved:12;
> > > + } hw_gen_event;
> > > + struct hw_cache_event {
> > > + uint32_t result_id:1;
> > > + uint32_t op_id:2;
> > > + uint32_t cache_id:13;
> > > + uint32_t event_type:4;
> > > + uint32_t reserved:12;
> > > + } hw_cache_event;
> > > + };
> > > + uint32_t event_idx;
> > > + };
> > > +};
> > > +
> > > +static const struct pmu_event_data pmu_hw_event_map[] = {
> > > + [PERF_COUNT_HW_CPU_CYCLES] = {.hw_gen_event = {
> > > + SBI_PMU_HW_CPU_CYCLES,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_INSTRUCTIONS] = {.hw_gen_event = {
> > > + SBI_PMU_HW_INSTRUCTIONS,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_CACHE_REFERENCES] = {.hw_gen_event = {
> > > + SBI_PMU_HW_CACHE_REFERENCES,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_CACHE_MISSES] = {.hw_gen_event = {
> > > + SBI_PMU_HW_CACHE_MISSES,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = {.hw_gen_event = {
> > > + SBI_PMU_HW_BRANCH_INSTRUCTIONS,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_BRANCH_MISSES] = {.hw_gen_event = {
> > > + SBI_PMU_HW_BRANCH_MISSES,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_BUS_CYCLES] = {.hw_gen_event = {
> > > + SBI_PMU_HW_BUS_CYCLES,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = {.hw_gen_event = {
> > > + SBI_PMU_HW_STALLED_CYCLES_FRONTEND,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_STALLED_CYCLES_BACKEND] = {.hw_gen_event = {
> > > + SBI_PMU_HW_STALLED_CYCLES_BACKEND,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > + [PERF_COUNT_HW_REF_CPU_CYCLES] = {.hw_gen_event = {
> > > + SBI_PMU_HW_REF_CPU_CYCLES,
> > > + SBI_PMU_EVENT_TYPE_HW, 0}},
> > > +};
> > > +
> > > +#define C(x) PERF_COUNT_HW_CACHE_##x
> > > +static const struct pmu_event_data pmu_cache_event_map[PERF_COUNT_HW_CACHE_MAX]
> > > +[PERF_COUNT_HW_CACHE_OP_MAX]
> > > +[PERF_COUNT_HW_CACHE_RESULT_MAX] = {
> > > + [C(L1D)] = {
> > > + [C(OP_READ)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_READ), C(L1D), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_READ), C(L1D), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_WRITE)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_WRITE), C(L1D), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_WRITE), C(L1D), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_PREFETCH)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_PREFETCH), C(L1D), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_PREFETCH), C(L1D), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + },
> > > + [C(L1I)] = {
> > > + [C(OP_READ)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_READ), C(L1I), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS), C(OP_READ),
> > > + C(L1I), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_WRITE)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_WRITE), C(L1I), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_WRITE), C(L1I), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_PREFETCH)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_PREFETCH), C(L1I), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_PREFETCH), C(L1I), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + },
> > > + [C(LL)] = {
> > > + [C(OP_READ)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_READ), C(LL), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_READ), C(LL), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_WRITE)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_WRITE), C(LL), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_WRITE), C(LL), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_PREFETCH)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_PREFETCH), C(LL), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_PREFETCH), C(LL), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + },
> > > + [C(DTLB)] = {
> > > + [C(OP_READ)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_READ), C(DTLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_READ), C(DTLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_WRITE)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_WRITE), C(DTLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_WRITE), C(DTLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_PREFETCH)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_PREFETCH), C(DTLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_PREFETCH), C(DTLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + },
> > > + [C(ITLB)] = {
> > > + [C(OP_READ)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_READ), C(ITLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_READ), C(ITLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_WRITE)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_WRITE), C(ITLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_WRITE), C(ITLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_PREFETCH)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_PREFETCH), C(ITLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_PREFETCH), C(ITLB), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + },
> > > + [C(BPU)] = {
> > > + [C(OP_READ)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_READ), C(BPU), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_READ), C(BPU), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_WRITE)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_WRITE), C(BPU), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_WRITE), C(BPU), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_PREFETCH)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_PREFETCH), C(BPU), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_PREFETCH), C(BPU), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + },
> > > + [C(NODE)] = {
> > > + [C(OP_READ)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_READ), C(NODE), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_READ), C(NODE), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_WRITE)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_WRITE), C(NODE), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_WRITE), C(NODE), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + [C(OP_PREFETCH)] = {
> > > + [C(RESULT_ACCESS)] = {.hw_cache_event = {C(RESULT_ACCESS),
> > > + C(OP_PREFETCH), C(NODE), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + [C(RESULT_MISS)] = {.hw_cache_event = {C(RESULT_MISS),
> > > + C(OP_PREFETCH), C(NODE), SBI_PMU_EVENT_TYPE_CACHE, 0}},
> > > + },
> > > + },
> > > +};
> > > +
> > > +static int pmu_sbi_ctr_get_width(int idx)
> > > +{
> > > + return pmu_ctr_list[idx].width;
> > > +}
> > > +
> > > +static int pmu_sbi_ctr_get_idx(struct perf_event *event)
> > > +{
> > > + struct hw_perf_event *hwc = &event->hw;
> > > + struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
> > > + struct cpu_hw_events *cpuc = this_cpu_ptr(rvpmu->hw_events);
> > > + struct sbiret ret;
> > > + int idx;
> > > + uint64_t cbase = 0;
> > > + uint64_t cmask = GENMASK_ULL(rvpmu->num_counters - 1, 0);
> > > + unsigned long cflags = 0;
> > > +
> > > + /* retrieve the available counter index */
> > > + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_CFG_MATCH, cbase, cmask,
> > > + cflags, hwc->event_base, hwc->config, 0);
> > > + if (ret.error) {
> > > + pr_debug("Not able to find a counter for event %lx config %llx\n",
> > > + hwc->event_base, hwc->config);
> > > + return sbi_err_map_linux_errno(ret.error);
> > > + }
> > > +
> > > + idx = ret.value;
> > > + if (idx >= rvpmu->num_counters || !pmu_ctr_list[idx].value)
> > > + return -ENOENT;
> > > +
> > > + /* Additional sanity check for the counter id */
> > > + if (!test_and_set_bit(idx, cpuc->used_event_ctrs))
> > > + return idx;
> > > + else
> > > + return -ENOENT;
> > > +}
> > > +
> > > +static void pmu_sbi_ctr_clear_idx(struct perf_event *event)
> > > +{
> > > +
> > > + struct hw_perf_event *hwc = &event->hw;
> > > + struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
> > > + struct cpu_hw_events *cpuc = this_cpu_ptr(rvpmu->hw_events);
> > > + int idx = hwc->idx;
> > > +
> > > + clear_bit(idx, cpuc->used_event_ctrs);
> > > +}
> > > +
> > > +static int pmu_event_find_cache(u64 config)
> > > +{
> > > + unsigned int cache_type, cache_op, cache_result, ret;
> > > +
> > > + cache_type = (config >> 0) & 0xff;
> > > + if (cache_type >= PERF_COUNT_HW_CACHE_MAX)
> > > + return -EINVAL;
> > > +
> > > + cache_op = (config >> 8) & 0xff;
> > > + if (cache_op >= PERF_COUNT_HW_CACHE_OP_MAX)
> > > + return -EINVAL;
> > > +
> > > + cache_result = (config >> 16) & 0xff;
> > > + if (cache_result >= PERF_COUNT_HW_CACHE_RESULT_MAX)
> > > + return -EINVAL;
> > > +
> > > + ret = pmu_cache_event_map[cache_type][cache_op][cache_result].event_idx;
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static bool pmu_sbi_is_fw_event(struct perf_event *event)
> > > +{
> > > + u32 type = event->attr.type;
> > > + u64 config = event->attr.config;
> > > +
> > > + if ((type == PERF_TYPE_RAW) && ((config >> 63) == 1))
> > > + return true;
> > > + else
> > > + return false;
> > > +}
> > > +
> > > +static int pmu_sbi_event_map(struct perf_event *event, u64 *econfig)
> > > +{
> > > + u32 type = event->attr.type;
> > > + u64 config = event->attr.config;
> > > + int bSoftware;
> > > + u64 raw_config_val;
> > > + int ret;
> > > +
> > > + switch (type) {
> > > + case PERF_TYPE_HARDWARE:
> > > + if (config >= PERF_COUNT_HW_MAX)
> > > + return -EINVAL;
> > > + ret = pmu_hw_event_map[event->attr.config].event_idx;
> > > + break;
> > > + case PERF_TYPE_HW_CACHE:
> > > + ret = pmu_event_find_cache(config);
> > > + break;
> > > + case PERF_TYPE_RAW:
> > > + /*
> > > + * As per SBI specification, the upper 7 bits must be unused for
> > > + * a raw event. Use the MSB (63b) to distinguish between hardware
> > > + * raw event and firmware events.
> > > + */
> > > + bSoftware = config >> 63;
> > > + raw_config_val = config & RISCV_PMU_RAW_EVENT_MASK;
> > > + if (bSoftware) {
> > > + if (raw_config_val < SBI_PMU_FW_MAX)
> > > + ret = (raw_config_val & 0xFFFF) |
> > > + (SBI_PMU_EVENT_TYPE_FW << 16);
> > > + else
> > > + return -EINVAL;
> > > + } else {
> > > + ret = RISCV_PMU_RAW_EVENT_IDX;
> > > + *econfig = raw_config_val;
> > > + }
> > > + break;
> > > + default:
> > > + ret = -EINVAL;
> > > + break;
> > > + }
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static u64 pmu_sbi_ctr_read(struct perf_event *event)
> > > +{
> > > + struct hw_perf_event *hwc = &event->hw;
> > > + int idx = hwc->idx;
> > > + struct sbiret ret;
> > > + union sbi_pmu_ctr_info info;
> > > + u64 val = 0;
> > > +
> > > + if (pmu_sbi_is_fw_event(event)) {
> > > + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_FW_READ,
> > > + hwc->idx, 0, 0, 0, 0, 0);
> > > + if (!ret.error)
> > > + val = ret.value;
> > > + } else {
> > > + info = pmu_ctr_list[idx];
> > > + val = riscv_pmu_ctr_read_csr(info.csr);
> > > + if (IS_ENABLED(CONFIG_32BIT))
> > > + val = ((u64)riscv_pmu_ctr_read_csr(info.csr + 0x80)) << 32 | val;
> > > + }
> > > +
> > > + return val;
> > > +}
> > > +
> > > +static void pmu_sbi_ctr_start(struct perf_event *event, u64 ival)
> > > +{
> > > + struct sbiret ret;
> > > + struct hw_perf_event *hwc = &event->hw;
> > > +
> > > + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_START, hwc->idx,
> > > + 1, 1, ival, 0, 0);
> > > + if (ret.error)
> > > + pr_err("Starting counter idx %d failed with error %d\n",
> > > + hwc->idx, sbi_err_map_linux_errno(ret.error));
> > > +}
> > > +
> > > +static void pmu_sbi_ctr_stop(struct perf_event *event)
> > > +{
> > > + struct sbiret ret;
> > > + struct hw_perf_event *hwc = &event->hw;
> > > + struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
> > > + struct cpu_hw_events *cpuc = this_cpu_ptr(rvpmu->hw_events);
> > > + unsigned long flag = 0;
> > > +
> > > + if (cpuc->events[hwc->idx] == NULL)
> > > + flag = SBI_PMU_STOP_FLAG_RESET;
> > > + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, hwc->idx, 1, flag, 0, 0, 0);
> > > + if (ret.error)
> > > + pr_err("Stopping counter idx %d failed with error %d\n",
> > > + hwc->idx, sbi_err_map_linux_errno(ret.error));
> > > +}
> > > +
> > > +static int pmu_sbi_find_num_ctrs(void)
> > > +{
> > > + struct sbiret ret;
> > > +
> > > + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_NUM_COUNTERS, 0, 0, 0, 0, 0, 0);
> > > + if (!ret.error)
> > > + return ret.value;
> > > + else
> > > + return sbi_err_map_linux_errno(ret.error);
> > > +}
> > > +
> > > +static int pmu_sbi_get_ctrinfo(int nctr)
> > > +{
> > > + struct sbiret ret;
> > > + int i, num_hw_ctr = 0, num_fw_ctr = 0;
> > > + union sbi_pmu_ctr_info cinfo;
> > > +
> > > + pmu_ctr_list = kzalloc(sizeof(*pmu_ctr_list) * nctr, GFP_KERNEL);
> > > + if (!pmu_ctr_list)
> > > + return -ENOMEM;
> > > +
> > > + for (i = 0; i <= nctr; i++) {
> > > + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_GET_INFO, i, 0, 0, 0, 0, 0);
> > > + if (ret.error)
> > > + /* The logical counter ids are not expected to be contiguous */
> > > + continue;
> > > + cinfo.value = ret.value;
> > > + if (cinfo.type == SBI_PMU_CTR_TYPE_FW)
> > > + num_fw_ctr++;
> > > + else
> > > + num_hw_ctr++;
> > > + pmu_ctr_list[i].value = cinfo.value;
> > > + }
> > > +
> > > + pr_info("There are %d firmware & %d hardware counters available\n",
> > > + num_fw_ctr, num_hw_ctr);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +static int pmu_sbi_starting_cpu(unsigned int cpu)
> > > +{
> > > + /* Enable the access for TIME csr only from the user mode now */
> > > + csr_write(CSR_SCOUNTEREN, 0x2);
> > Would it be possible to also enable CYCLE csr here (and I guess same
> > would propagate to mcounteren logic in the opensbi patches)? Are there
> > any security concerns in allowing applications to read it directly?
>
> If CYCLE csr is always enabled then a process can get cycle count of
> all process and underlying kernel. This means process A can now
> estimate code path taken by process B based on observing variations
> in CYCLE csr values. This certainly seems like a back-door channel
> being opened up.
>
> Ideally, a process should only see CPU cycles consumed by the
> process itself. Same rationale applies to Guest/VM as well.
>
> >
> > It would be useful given that the frequency of TIME is not fixed in spec
> > and it may not be enough for a rdtsc-like counter. In such cases CYCLE
> > csr might be useful to userspace applications (i.e. DPDK) with obvious
> > limitations such as gating via WFI or value changes when using perf.
>
> CYCLE csr frequency is also not fixed. In fact, CYCLE csr frequency
> is same as CPU frequency and RISC-V platforms might support
> CPU frequency scaling as well in which case CYCLE csr frequency
> can change at runtime.
>
> On other hand, it is much simpler to expose timer frequency to
> user space via procfs or sysfs. In fact, RISC-V platform will always
> have fixed frequency for TIME csr irrespective to underlying CPU
> frequency.
>
> >
> > For context: there was a similar situation with arm64 at the point of
> > DPDK port to that arch. Armv7-A standardized their timer (CNTVCT) but
> > not its frequency which usually was ~100MHz. The PMU cycle counter
> > (PMCCNTR) was by default disabled for read from userspace (EL0). This
> > required DPDK folks to create a kernel module to enable the PMCCNTR in
> > userspace so that they could implement high-resolution rte_rdtsc() call.
> > This got fixed in Armv8.6-A which specified the timer counter frequency
> > to be 1GHz.
> >
> > If the CYCLE csr remains S-mode private, I will have to effectively
> > resort to the same kernel-module trick as arm64 in the RISC-V DPDK port.
> > Alternatively perhaps a sysfs knob or driver parameter could be added to
> > enable the CYCLE csr in U-mode?
>
> Before we think about sysfs knob or driver parameter, I would suggest
> you to explore approaches of knowing timer frequency in DPDK.
If device tree is exposed via procfs then you can know the TIME csr
frequency by reading:
/proc/device-tree/cpus/timebase-frequency
Regards,
Anup
>
> Regards,
> Anup
>
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +static int pmu_sbi_dying_cpu(unsigned int cpu)
> > > +{
> > > + /* Disable all counters access for user mode now */
> > > + csr_write(CSR_SCOUNTEREN, 0x0);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +
> > > +static int pmu_sbi_device_probe(struct platform_device *pdev)
> > > +{
> > > + struct riscv_pmu *pmu = NULL;
> > > + int num_counters;
> > > +
> > > + pmu = riscv_pmu_alloc();
> > > + if (!pmu)
> > > + return -ENOMEM;
> > > +
> > > + if (((sbi_major_version() == 0) && (sbi_minor_version() < 3)) ||
> > > + sbi_probe_extension(SBI_EXT_PMU) <= 0) {
> > > + /* Fall back to the legacy implementation */
> > > + riscv_pmu_legacy_init(pmu);
> > > + return 0;
> > > + }
> > > +
> > > + pr_info("SBI PMU extension is available\n");
> > > +
> > > + num_counters = pmu_sbi_find_num_ctrs();
> > > + if (num_counters < 0) {
> > > + pr_err("SBI PMU extension doesn't provide any counters\n");
> > > + return -ENODEV;
> > > + }
> > > +
> > > + /* cache all the information about counters now */
> > > + if (pmu_sbi_get_ctrinfo(num_counters))
> > > + return -ENODEV;
> > > +
> > > + pmu->num_counters = num_counters;
> > > + pmu->ctr_start = pmu_sbi_ctr_start;
> > > + pmu->ctr_stop = pmu_sbi_ctr_stop;
> > > + pmu->event_map = pmu_sbi_event_map;
> > > + pmu->ctr_get_idx = pmu_sbi_ctr_get_idx;
> > > + pmu->ctr_get_width = pmu_sbi_ctr_get_width;
> > > + pmu->ctr_clear_idx = pmu_sbi_ctr_clear_idx;
> > > + pmu->ctr_read = pmu_sbi_ctr_read;
> > > +
> > > + perf_pmu_register(&pmu->pmu, "cpu", PERF_TYPE_RAW);
> > > +
> > > + cpuhp_setup_state(CPUHP_AP_PERF_RISCV_STARTING,
> > > + "perf/riscv/pmu:starting",
> > > + pmu_sbi_starting_cpu, pmu_sbi_dying_cpu);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +static struct platform_driver pmu_sbi_driver = {
> > > + .probe = pmu_sbi_device_probe,
> > > + .driver = {
> > > + .name = RISCV_PMU_PDEV_NAME,
> > > + },
> > > +};
> > > +
> > > +static int __init pmu_sbi_devinit(void)
> > > +{
> > > + int ret;
> > > + struct platform_device *pdev;
> > > +
> > > + ret = platform_driver_register(&pmu_sbi_driver);
> > > + if (ret)
> > > + return ret;
> > > +
> > > + pdev = platform_device_register_simple(RISCV_PMU_PDEV_NAME, -1, NULL, 0);
> > > + if (IS_ERR(pdev)) {
> > > + platform_driver_unregister(&pmu_sbi_driver);
> > > + return PTR_ERR(pdev);
> > > + }
> > > +
> > > + return ret;
> > > +}
> > > +device_initcall(pmu_sbi_devinit)
> > > --
> > > 2.25.1
> > >
> > >
> > > _______________________________________________
> > > linux-riscv mailing list
> > > linux-riscv at lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> >
> > --
> > Best Regards,
> > Stanislaw Kardach
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