[PATCH v2 1/2] perf: riscv: preliminary RISC-V support

Alan Kao
2018-04-02T12:31:57Z

This patch provide a basic PMU, riscv_base_pmu, which supports two
general hardware event, instructions and cycles. Furthermore, this
PMU serves as a reference implementation to ease the portings in
the future.

riscv_base_pmu should be able to run on any RISC-V machine that
conforms to the Priv-Spec. Note that the latest qemu model hasn't
fully support a proper behavior of Priv-Spec 1.10 yet, but work
around should be easy with very small fixes. Please check
https://github.com/riscv/riscv-qemu/pull/115 for future updates.

Cc: Nick Hu <nickhu@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Signed-off-by: Alan Kao <alankao@andestech.com>
---
arch/riscv/Kconfig | 12 +
arch/riscv/include/asm/perf_event.h | 76 +++++-
arch/riscv/kernel/Makefile | 1 +
arch/riscv/kernel/perf_event.c | 468 ++++++++++++++++++++++++++++++++++++
4 files changed, 553 insertions(+), 4 deletions(-)
create mode 100644 arch/riscv/kernel/perf_event.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index c22ebe08e902..3fbf19456c9a 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -203,6 +203,18 @@ config RISCV_ISA_C
config RISCV_ISA_A
def_bool y

+menu "PMU type"
+ depends on PERF_EVENTS
+
+config RISCV_BASE_PMU
+ bool "Base Performance Monitoring Unit"
+ def_bool y
+ help
+ A base PMU that serves as a reference implementation and has limited
+ feature of perf.
+
+endmenu
+
endmenu

menu "Kernel type"
diff --git a/arch/riscv/include/asm/perf_event.h b/arch/riscv/include/asm/perf_event.h
index e13d2ff29e83..98e2efb02d25 100644
--- a/arch/riscv/include/asm/perf_event.h
+++ b/arch/riscv/include/asm/perf_event.h
@@ -1,13 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2018 SiFive
+ * Copyright (C) 2018 Andes Technology Corporation
*
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public Licence
- * as published by the Free Software Foundation; either version
- * 2 of the Licence, or (at your option) any later version.
*/

#ifndef _ASM_RISCV_PERF_EVENT_H
#define _ASM_RISCV_PERF_EVENT_H

+#include <linux/perf_event.h>
+#include <linux/ptrace.h>
+
+#define RISCV_BASE_COUNTERS 2
+
+/*
+ * The RISCV_MAX_COUNTERS parameter should be specified.
+ */
+
+#ifdef CONFIG_RISCV_BASE_PMU
+#define RISCV_MAX_COUNTERS 2
+#endif
+
+#ifndef RISCV_MAX_COUNTERS
+#error "Please provide a valid RISCV_MAX_COUNTERS for the PMU."
+#endif
+
+/*
+ * These are the indexes of bits in counteren register *minus* 1,
+ * except for cycle. It would be coherent if it can directly mapped
+ * to counteren bit definition, but there is a *time* register at
+ * counteren[1]. Per-cpu structure is scarce resource here.
+ *
+ * According to the spec, an implementation can support counter up to
+ * mhpmcounter31, but many high-end processors has at most 6 general
+ * PMCs, we give the definition to MHPMCOUNTER8 here.
+ */
+#define RISCV_PMU_CYCLE 0
+#define RISCV_PMU_INSTRET 1
+#define RISCV_PMU_MHPMCOUNTER3 2
+#define RISCV_PMU_MHPMCOUNTER4 3
+#define RISCV_PMU_MHPMCOUNTER5 4
+#define RISCV_PMU_MHPMCOUNTER6 5
+#define RISCV_PMU_MHPMCOUNTER7 6
+#define RISCV_PMU_MHPMCOUNTER8 7
+
+#define RISCV_OP_UNSUPP (-EOPNOTSUPP)
+
+struct cpu_hw_events {
+ /* # currently enabled events*/
+ int n_events;
+ /* currently enabled events */
+ struct perf_event *events[RISCV_MAX_COUNTERS];
+ /* vendor-defined PMU data */
+ void *platform;
+};
+
+struct riscv_pmu {
+ struct pmu *pmu;
+
+ /* generic hw/cache events table */
+ const int *hw_events;
+ const int (*cache_events)[PERF_COUNT_HW_CACHE_MAX]
+ [PERF_COUNT_HW_CACHE_OP_MAX]
+ [PERF_COUNT_HW_CACHE_RESULT_MAX];
+ /* method used to map hw/cache events */
+ int (*map_hw_event)(u64 config);
+ int (*map_cache_event)(u64 config);
+
+ /* max generic hw events in map */
+ int max_events;
+ /* number total counters, 2(base) + x(general) */
+ int num_counters;
+ /* the width of the counter */
+ int counter_width;
+
+ /* vendor-defined PMU features */
+ void *platform;
+};
+
#endif /* _ASM_RISCV_PERF_EVENT_H */
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index ffa439d4a364..f50d19816757 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -39,5 +39,6 @@ obj-$(CONFIG_MODULE_SECTIONS) += module-sections.o
obj-$(CONFIG_FUNCTION_TRACER) += mcount.o
obj-$(CONFIG_DYNAMIC_FTRACE) += mcount-dyn.o
obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
+obj-$(CONFIG_PERF_EVENTS) += perf_event.o

clean:
diff --git a/arch/riscv/kernel/perf_event.c b/arch/riscv/kernel/perf_event.c
new file mode 100644
index 000000000000..cac4abd0a884
--- /dev/null
+++ b/arch/riscv/kernel/perf_event.c
@@ -0,0 +1,468 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
+ * Copyright (C) 2008-2009 Red Hat, Inc., Ingo Molnar
+ * Copyright (C) 2009 Jaswinder Singh Rajput
+ * Copyright (C) 2009 Advanced Micro Devices, Inc., Robert Richter
+ * Copyright (C) 2008-2009 Red Hat, Inc., Peter Zijlstra
+ * Copyright (C) 2009 Intel Corporation, <markus.t.metzger@intel.com>
+ * Copyright (C) 2009 Google, Inc., Stephane Eranian
+ * Copyright 2014 Tilera Corporation. All Rights Reserved.
+ * Copyright (C) 2018 Andes Technology Corporation
+ *
+ * Perf_events support for RISC-V platforms.
+ *
+ * Since the spec. (as of now, Priv-Spec 1.10) does not provide enough
+ * functionality for perf event to fully work, this file provides
+ * the very basic framework only.
+ *
+ * For platform portings, please check Documentations/riscv/pmu.txt.
+ *
+ * The Copyright line includes x86 and tile ones.
+ */
+
+#include <linux/kprobes.h>
+#include <linux/kernel.h>
+#include <linux/kdebug.h>
+#include <linux/mutex.h>
+#include <linux/bitmap.h>
+#include <linux/irq.h>
+#include <linux/interrupt.h>
+#include <linux/perf_event.h>
+#include <linux/atomic.h>
+#include <asm/perf_event.h>
+
+static const struct riscv_pmu *riscv_pmu __read_mostly;
+static DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events);
+
+/*
+ * Hardware & cache maps and their methods
+ */
+
+static const int riscv_hw_event_map[] = {
+ [PERF_COUNT_HW_CPU_CYCLES] = RISCV_PMU_CYCLE,
+ [PERF_COUNT_HW_INSTRUCTIONS] = RISCV_PMU_INSTRET,
+ [PERF_COUNT_HW_CACHE_REFERENCES] = RISCV_OP_UNSUPP,
+ [PERF_COUNT_HW_CACHE_MISSES] = RISCV_OP_UNSUPP,
+ [PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = RISCV_OP_UNSUPP,
+ [PERF_COUNT_HW_BRANCH_MISSES] = RISCV_OP_UNSUPP,
+ [PERF_COUNT_HW_BUS_CYCLES] = RISCV_OP_UNSUPP,
+};
+
+#define C(x) PERF_COUNT_HW_CACHE_##x
+static const int riscv_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)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_WRITE)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_PREFETCH)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ },
+ [C(L1I)] = {
+ [C(OP_READ)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_WRITE)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_PREFETCH)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ },
+ [C(LL)] = {
+ [C(OP_READ)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_WRITE)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_PREFETCH)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ },
+ [C(DTLB)] = {
+ [C(OP_READ)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_WRITE)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_PREFETCH)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ },
+ [C(ITLB)] = {
+ [C(OP_READ)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_WRITE)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_PREFETCH)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ },
+ [C(BPU)] = {
+ [C(OP_READ)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_WRITE)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ [C(OP_PREFETCH)] = {
+ [C(RESULT_ACCESS)] = RISCV_OP_UNSUPP,
+ [C(RESULT_MISS)] = RISCV_OP_UNSUPP,
+ },
+ },
+};
+
+static int riscv_map_hw_event(u64 config)
+{
+ if (config >= riscv_pmu->max_events)
+ return -EINVAL;
+
+ return riscv_pmu->hw_events[config];
+}
+
+int riscv_map_cache_decode(u64 config, unsigned int *type,
+ unsigned int *op, unsigned int *result)
+{
+ return -ENOENT;
+}
+
+static int riscv_map_cache_event(u64 config)
+{
+ unsigned int type, op, result;
+ int err = -ENOENT;
+ int code;
+
+ err = riscv_map_cache_decode(config, &type, &op, &result);
+ if (!riscv_pmu->cache_events || err)
+ return err;
+
+ if (type >= PERF_COUNT_HW_CACHE_MAX ||
+ op >= PERF_COUNT_HW_CACHE_OP_MAX ||
+ result >= PERF_COUNT_HW_CACHE_RESULT_MAX)
+ return -EINVAL;
+
+ code = (*riscv_pmu->cache_events)[type][op][result];
+ if (code == RISCV_OP_UNSUPP)
+ return -EINVAL;
+
+ return code;
+}
+
+/*
+ * Low-level functions: reading/writing counters
+ */
+
+static inline u64 read_counter(int idx)
+{
+ u64 val = 0;
+
+ switch (idx) {
+ case RISCV_PMU_CYCLE:
+ val = csr_read(cycle);
+ break;
+ case RISCV_PMU_INSTRET:
+ val = csr_read(instret);
+ break;
+ default:
+ WARN_ON_ONCE(idx < 0 || idx > RISCV_MAX_COUNTERS);
+ return -EINVAL;
+ }
+
+ return val;
+}
+
+static inline void write_counter(int idx, u64 value)
+{
+ /* currently not supported */
+}
+
+/*
+ * pmu->read: read and update the counter
+ *
+ * Other architectures' implementation often have a xxx_perf_event_update
+ * routine, which can return counter values when called in the IRQ, but
+ * return void when being called by the pmu->read method.
+ */
+static void riscv_pmu_read(struct perf_event *event)
+{
+ struct hw_perf_event *hwc = &event->hw;
+ u64 prev_raw_count, new_raw_count;
+ u64 oldval;
+ int idx = hwc->idx;
+ u64 delta;
+
+ do {
+ prev_raw_count = local64_read(&hwc->prev_count);
+ new_raw_count = read_counter(idx);
+
+ oldval = local64_cmpxchg(&hwc->prev_count, prev_raw_count,
+ new_raw_count);
+ } while (oldval != prev_raw_count);
+
+ /*
+ * delta is the value to update the counter we maintain in the kernel.
+ */
+ delta = (new_raw_count - prev_raw_count) &
+ ((1ULL << riscv_pmu->counter_width) - 1);
+ local64_add(delta, &event->count);
+ /*
+ * Something like local64_sub(delta, &hwc->period_left) here is
+ * needed if there is an interrupt for perf.
+ */
+}
+
+/*
+ * State transition functions:
+ *
+ * stop()/start() & add()/del()
+ */
+
+/*
+ * pmu->stop: stop the counter
+ */
+static void riscv_pmu_stop(struct perf_event *event, int flags)
+{
+ struct hw_perf_event *hwc = &event->hw;
+
+ WARN_ON_ONCE(hwc->state & PERF_HES_STOPPED);
+ hwc->state |= PERF_HES_STOPPED;
+
+ if ((flags & PERF_EF_UPDATE) && !(hwc->state & PERF_HES_UPTODATE)) {
+ riscv_pmu_read(event);
+ hwc->state |= PERF_HES_UPTODATE;
+ }
+}
+
+/*
+ * pmu->start: start the event.
+ */
+static void riscv_pmu_start(struct perf_event *event, int flags)
+{
+ struct hw_perf_event *hwc = &event->hw;
+
+ if (WARN_ON_ONCE(!(event->hw.state & PERF_HES_STOPPED)))
+ return;
+
+ if (flags & PERF_EF_RELOAD) {
+ WARN_ON_ONCE(!(event->hw.state & PERF_HES_UPTODATE));
+
+ /*
+ * Set the counter to the period to the next interrupt here,
+ * if you have any.
+ */
+ }
+
+ hwc->state = 0;
+ perf_event_update_userpage(event);
+
+ /*
+ * Since we cannot write to counters, this serves as an initialization
+ * to the delta-mechanism in pmu->read(); otherwise, the delta would be
+ * wrong when pmu->read is called for the first time.
+ */
+ local64_set(&hwc->prev_count, read_counter(hwc->idx));
+}
+
+/*
+ * pmu->add: add the event to PMU.
+ */
+static int riscv_pmu_add(struct perf_event *event, int flags)
+{
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+ struct hw_perf_event *hwc = &event->hw;
+
+ if (cpuc->n_events == riscv_pmu->num_counters)
+ return -ENOSPC;
+
+ /*
+ * We don't have general conunters, so no binding-event-to-counter
+ * process here.
+ *
+ * Indexing using hwc->config generally not works, since config may
+ * contain extra information, but here the only info we have in
+ * hwc->config is the event index.
+ */
+ hwc->idx = hwc->config;
+ cpuc->events[hwc->idx] = event;
+ cpuc->n_events++;
+
+ hwc->state = PERF_HES_UPTODATE | PERF_HES_STOPPED;
+
+ if (flags & PERF_EF_START)
+ riscv_pmu_start(event, PERF_EF_RELOAD);
+
+ return 0;
+}
+
+/*
+ * pmu->del: delete the event from PMU.
+ */
+static void riscv_pmu_del(struct perf_event *event, int flags)
+{
+ struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+ struct hw_perf_event *hwc = &event->hw;
+
+ cpuc->events[hwc->idx] = NULL;
+ cpuc->n_events--;
+ riscv_pmu_stop(event, PERF_EF_UPDATE);
+ perf_event_update_userpage(event);
+}
+
+/*
+ * Interrupt
+ */
+
+static DEFINE_MUTEX(pmc_reserve_mutex);
+typedef void (*perf_irq_t)(void *riscv_perf_irq);
+perf_irq_t perf_irq;
+
+void riscv_pmu_handle_irq(void *riscv_perf_irq)
+{
+}
+
+static perf_irq_t reserve_pmc_hardware(void)
+{
+ perf_irq_t old;
+
+ mutex_lock(&pmc_reserve_mutex);
+ old = perf_irq;
+ perf_irq = &riscv_pmu_handle_irq;
+ mutex_unlock(&pmc_reserve_mutex);
+
+ return old;
+}
+
+void release_pmc_hardware(void)
+{
+ mutex_lock(&pmc_reserve_mutex);
+ perf_irq = NULL;
+ mutex_unlock(&pmc_reserve_mutex);
+}
+
+/*
+ * Event Initialization
+ */
+
+static atomic_t riscv_active_events;
+
+static void riscv_event_destroy(struct perf_event *event)
+{
+ if (atomic_dec_return(&riscv_active_events) == 0)
+ release_pmc_hardware();
+}
+
+static int riscv_event_init(struct perf_event *event)
+{
+ struct perf_event_attr *attr = &event->attr;
+ struct hw_perf_event *hwc = &event->hw;
+ perf_irq_t old_irq_handler = NULL;
+ int code;
+
+ if (atomic_inc_return(&riscv_active_events) == 1)
+ old_irq_handler = reserve_pmc_hardware();
+
+ if (old_irq_handler) {
+ pr_warn("PMC hardware busy (reserved by oprofile)\n");
+ atomic_dec(&riscv_active_events);
+ return -EBUSY;
+ }
+
+ switch (event->attr.type) {
+ case PERF_TYPE_HARDWARE:
+ code = riscv_pmu->map_hw_event(attr->config);
+ break;
+ case PERF_TYPE_HW_CACHE:
+ code = riscv_pmu->map_cache_event(attr->config);
+ break;
+ case PERF_TYPE_RAW:
+ return -EOPNOTSUPP;
+ default:
+ return -ENOENT;
+ }
+
+ event->destroy = riscv_event_destroy;
+ if (code < 0) {
+ event->destroy(event);
+ return code;
+ }
+
+ /*
+ * idx is set to -1 because the index of a general event should not be
+ * decided until binding to some counter in pmu->add().
+ *
+ * But since we don't have such support, later in pmu->add(), we just
+ * use hwc->config as the index instead.
+ */
+ hwc->config = code;
+ hwc->idx = -1;
+
+ return 0;
+}
+
+/*
+ * Initialization
+ */
+
+static struct pmu min_pmu = {
+ .name = "riscv-base",
+ .event_init = riscv_event_init,
+ .add = riscv_pmu_add,
+ .del = riscv_pmu_del,
+ .start = riscv_pmu_start,
+ .stop = riscv_pmu_stop,
+ .read = riscv_pmu_read,
+};
+
+static const struct riscv_pmu riscv_base_pmu = {
+ .pmu = &min_pmu,
+ .max_events = ARRAY_SIZE(riscv_hw_event_map),
+ .map_hw_event = riscv_map_hw_event,
+ .hw_events = riscv_hw_event_map,
+ .map_cache_event = riscv_map_cache_event,
+ .cache_events = &riscv_cache_event_map,
+ .counter_width = 63,
+ .num_counters = RISCV_BASE_COUNTERS + 0,
+};
+
+struct pmu * __weak __init riscv_init_platform_pmu(void)
+{
+ riscv_pmu = &riscv_base_pmu;
+ return riscv_pmu->pmu;
+}
+
+int __init init_hw_perf_events(void)
+{
+ struct pmu *pmu = riscv_init_platform_pmu();
+
+ perf_irq = NULL;
+ perf_pmu_register(pmu, "cpu", PERF_TYPE_RAW);
+ return 0;
+}
+arch_initcall(init_hw_perf_events);
--
2.16.2