Re: [PATCH v5 06/22] drivers/perf: riscv: Implement SBI PMU snapshot function

Atish Patra
2024-04-10T22:29:25Z

On 4/4/24 04:52, Andrew Jones wrote:
> On Wed, Apr 03, 2024 at 01:04:35AM -0700, Atish Patra wrote:
>> SBI v2.0 SBI introduced PMU snapshot feature which adds the following
>> features.
>>
>> 1. Read counter values directly from the shared memory instead of
>> csr read.
>> 2. Start multiple counters with initial values with one SBI call.
>>
>> These functionalities optimizes the number of traps to the higher
>> privilege mode. If the kernel is in VS mode while the hypervisor
>> deploy trap & emulate method, this would minimize all the hpmcounter
>> CSR read traps. If the kernel is running in S-mode, the benefits
>> reduced to CSR latency vs DRAM/cache latency as there is no trap
>> involved while accessing the hpmcounter CSRs.
>>
>> In both modes, it does saves the number of ecalls while starting
>> multiple counter together with an initial values. This is a likely
>> scenario if multiple counters overflow at the same time.
>>
>> Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
>> Reviewed-by: Anup Patel <anup@brainfault.org>
>> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
>> Signed-off-by: Atish Patra <atishp@rivosinc.com>
>> ---
>> drivers/perf/riscv_pmu.c | 1 +
>> drivers/perf/riscv_pmu_sbi.c | 216 +++++++++++++++++++++++++++++++--
>> include/linux/perf/riscv_pmu.h | 6 +
>> 3 files changed, 211 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
>> index c78a6fd6c57f..3a941b2c3888 100644
>> --- a/drivers/perf/riscv_pmu.c
>> +++ b/drivers/perf/riscv_pmu.c
>> @@ -404,6 +404,7 @@ struct riscv_pmu *riscv_pmu_alloc(void)
>> cpuc->n_events = 0;
>> for (i = 0; i < RISCV_MAX_COUNTERS; i++)
>> cpuc->events[i] = NULL;
>> + cpuc->snapshot_addr = NULL;
>> }
>> pmu->pmu = (struct pmu) {
>> .event_init = riscv_pmu_event_init,
>> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
>> index a83ae82301e3..8c3475d55433 100644
>> --- a/drivers/perf/riscv_pmu_sbi.c
>> +++ b/drivers/perf/riscv_pmu_sbi.c
>> @@ -58,6 +58,9 @@ PMU_FORMAT_ATTR(event, "config:0-47");
>> PMU_FORMAT_ATTR(firmware, "config:63");
>>
>> static bool sbi_v2_available;
>> +static DEFINE_STATIC_KEY_FALSE(sbi_pmu_snapshot_available);
>> +#define sbi_pmu_snapshot_available() \
>> + static_branch_unlikely(&sbi_pmu_snapshot_available)
>>
>> static struct attribute *riscv_arch_formats_attr[] = {
>> &format_attr_event.attr,
>> @@ -508,14 +511,108 @@ static int pmu_sbi_event_map(struct perf_event *event, u64 *econfig)
>> return ret;
>> }
>>
>> +static void pmu_sbi_snapshot_free(struct riscv_pmu *pmu)
>> +{
>> + int cpu;
>> +
>> + for_each_possible_cpu(cpu) {
>> + struct cpu_hw_events *cpu_hw_evt = per_cpu_ptr(pmu->hw_events, cpu);
>> +
>> + if (!cpu_hw_evt->snapshot_addr)
>> + continue;
>> +
>> + free_page((unsigned long)cpu_hw_evt->snapshot_addr);
>> + cpu_hw_evt->snapshot_addr = NULL;
>> + cpu_hw_evt->snapshot_addr_phys = 0;
>> + }
>> +}
>> +
>> +static int pmu_sbi_snapshot_alloc(struct riscv_pmu *pmu)
>> +{
>> + int cpu;
>> + struct page *snapshot_page;
>> +
>> + for_each_possible_cpu(cpu) {
>> + struct cpu_hw_events *cpu_hw_evt = per_cpu_ptr(pmu->hw_events, cpu);
>> +
>> + if (cpu_hw_evt->snapshot_addr)
>> + continue;
>> +
>> + snapshot_page = alloc_page(GFP_ATOMIC | __GFP_ZERO);
>> + if (!snapshot_page) {
>> + pmu_sbi_snapshot_free(pmu);
>> + return -ENOMEM;
>> + }
>> + cpu_hw_evt->snapshot_addr = page_to_virt(snapshot_page);
>> + cpu_hw_evt->snapshot_addr_phys = page_to_phys(snapshot_page);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int pmu_sbi_snapshot_disable(void)
>> +{
>> + struct sbiret ret;
>> +
>> + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_SNAPSHOT_SET_SHMEM, -1,
>> + -1, 0, 0, 0, 0);
>> + if (ret.error) {
>> + pr_warn("failed to disable snapshot shared memory\n");
>> + return sbi_err_map_linux_errno(ret.error);
>> + }
>
> Also need to set snapshot_set_done to false, but I'm not yet convinced

Done.

> that we need snapshot_set_done, especially if we don't allow
> snapshot_addr_phys to be zero, since zero can then mean set-not-done,
> but ~0UL is probably a better invalid physical address choice than zero.
>

Agreed. But I don't see any benefit either way. snapshot_set_done is
just more explicit way of doing the same thing without interpreting what
zero means.

If you think there is a benefit or you feel storngly about it, I can
change it you suggested approach.

Btw, I just realized that you had a comment about this in v4 as well.
Sorry I missed that and did not reply there.

>> +
>> + return 0;
>> +}
>> +
>> +static int pmu_sbi_snapshot_setup(struct riscv_pmu *pmu, int cpu)
>> +{
>> + struct cpu_hw_events *cpu_hw_evt;
>> + struct sbiret ret = {0};
>> +
>> + cpu_hw_evt = per_cpu_ptr(pmu->hw_events, cpu);
>> + if (!cpu_hw_evt->snapshot_addr_phys)
>> + return -EINVAL;
>> +
>> + if (cpu_hw_evt->snapshot_set_done)
>> + return 0;
>> +
>> + if (IS_ENABLED(CONFIG_32BIT))
>> + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_SNAPSHOT_SET_SHMEM,
>> + cpu_hw_evt->snapshot_addr_phys,
>> + (u64)(cpu_hw_evt->snapshot_addr_phys) >> 32, 0, 0, 0, 0);
>> + else
>> + ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_SNAPSHOT_SET_SHMEM,
>> + cpu_hw_evt->snapshot_addr_phys, 0, 0, 0, 0, 0);
>> +
>> + /* Free up the snapshot area memory and fall back to SBI PMU calls without snapshot */
>> + if (ret.error) {
>> + if (ret.error != SBI_ERR_NOT_SUPPORTED)
>> + pr_warn("pmu snapshot setup failed with error %ld\n", ret.error);
>> + return sbi_err_map_linux_errno(ret.error);
>> + }
>> +
>> + cpu_hw_evt->snapshot_set_done = true;
>> +
>> + return 0;
>> +}
>> +
>> static u64 pmu_sbi_ctr_read(struct perf_event *event)
>> {
>> struct hw_perf_event *hwc = &event->hw;
>> int idx = hwc->idx;
>> struct sbiret ret;
>> u64 val = 0;
>> + struct riscv_pmu *pmu = to_riscv_pmu(event->pmu);
>> + struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
>> + struct riscv_pmu_snapshot_data *sdata = cpu_hw_evt->snapshot_addr;
>> union sbi_pmu_ctr_info info = pmu_ctr_list[idx];
>>
>> + /* Read the value from the shared memory directly */
>> + if (sbi_pmu_snapshot_available()) {
>> + val = sdata->ctr_values[idx];
>> + return val;
>> + }
>> +
>> 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);
>> @@ -565,6 +662,7 @@ static void pmu_sbi_ctr_start(struct perf_event *event, u64 ival)
>> struct hw_perf_event *hwc = &event->hw;
>> unsigned long flag = SBI_PMU_START_FLAG_SET_INIT_VALUE;
>>
>> + /* There is no benefit setting SNAPSHOT FLAG for a single counter */
>> #if defined(CONFIG_32BIT)
>> ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_START, hwc->idx,
>> 1, flag, ival, ival >> 32, 0);
>> @@ -585,16 +683,36 @@ static void pmu_sbi_ctr_stop(struct perf_event *event, unsigned long flag)
>> {
>> struct sbiret ret;
>> struct hw_perf_event *hwc = &event->hw;
>> + struct riscv_pmu *pmu = to_riscv_pmu(event->pmu);
>> + struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
>> + struct riscv_pmu_snapshot_data *sdata = cpu_hw_evt->snapshot_addr;
>>
>> if ((hwc->flags & PERF_EVENT_FLAG_USER_ACCESS) &&
>> (hwc->flags & PERF_EVENT_FLAG_USER_READ_CNT))
>> pmu_sbi_reset_scounteren((void *)event);
>>
>> + if (sbi_pmu_snapshot_available())
>> + flag |= SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT;
>> +
>> ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, hwc->idx, 1, flag, 0, 0, 0);
>> - if (ret.error && (ret.error != SBI_ERR_ALREADY_STOPPED) &&
>> - flag != SBI_PMU_STOP_FLAG_RESET)
>> + if (!ret.error && sbi_pmu_snapshot_available()) {
>> + /*
>> + * The counter snapshot is based on the index base specified by hwc->idx.
>> + * The actual counter value is updated in shared memory at index 0 when counter
>> + * mask is 0x01. To ensure accurate counter values, it's necessary to transfer
>> + * the counter value to shared memory. However, if hwc->idx is zero, the counter
>> + * value is already correctly updated in shared memory, requiring no further
>> + * adjustment.
>> + */
>> + if (hwc->idx > 0) {
>> + sdata->ctr_values[hwc->idx] = sdata->ctr_values[0];
>> + sdata->ctr_values[0] = 0;
>> + }
>> + } else if (ret.error && (ret.error != SBI_ERR_ALREADY_STOPPED) &&
>> + flag != SBI_PMU_STOP_FLAG_RESET) {
>> 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)
>> @@ -652,10 +770,14 @@ static inline void pmu_sbi_stop_all(struct riscv_pmu *pmu)
>> static inline void pmu_sbi_stop_hw_ctrs(struct riscv_pmu *pmu)
>> {
>> struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
>> + unsigned long flag = 0;
>> +
>> + if (sbi_pmu_snapshot_available())
>> + flag = SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT;
>>
>> /* No need to check the error here as we can't do anything about the error */
>> sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_STOP, 0,
>> - cpu_hw_evt->used_hw_ctrs[0], 0, 0, 0, 0);
>> + cpu_hw_evt->used_hw_ctrs[0], flag, 0, 0, 0);
>> }
>>
>> /*
>> @@ -664,11 +786,10 @@ static inline void pmu_sbi_stop_hw_ctrs(struct riscv_pmu *pmu)
>> * while the overflowed counters need to be started with updated initialization
>> * value.
>> */
>> -static inline void pmu_sbi_start_overflow_mask(struct riscv_pmu *pmu,
>> - unsigned long ctr_ovf_mask)
>> +static noinline void pmu_sbi_start_ovf_ctrs_sbi(struct cpu_hw_events *cpu_hw_evt,
>> + unsigned long ctr_ovf_mask)
>> {
>> int idx = 0;
>> - struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
>> struct perf_event *event;
>> unsigned long flag = SBI_PMU_START_FLAG_SET_INIT_VALUE;
>> unsigned long ctr_start_mask = 0;
>> @@ -703,6 +824,48 @@ static inline void pmu_sbi_start_overflow_mask(struct riscv_pmu *pmu,
>> }
>> }
>>
>> +static noinline void pmu_sbi_start_ovf_ctrs_snapshot(struct cpu_hw_events *cpu_hw_evt,
>> + unsigned long ctr_ovf_mask)
>> +{
>> + int idx = 0;
>> + struct perf_event *event;
>> + unsigned long flag = SBI_PMU_START_FLAG_INIT_SNAPSHOT;
>> + u64 max_period, init_val = 0;
>> + struct hw_perf_event *hwc;
>> + struct riscv_pmu_snapshot_data *sdata = cpu_hw_evt->snapshot_addr;
>> +
>> + for_each_set_bit(idx, cpu_hw_evt->used_hw_ctrs, RISCV_MAX_COUNTERS) {
>> + if (ctr_ovf_mask & (BIT(idx))) {
>
> Unnecessary () around BIT()
>

Fixed.

>> + event = cpu_hw_evt->events[idx];
>> + hwc = &event->hw;
>> + max_period = riscv_pmu_ctr_get_width_mask(event);
>> + init_val = local64_read(&hwc->prev_count) & max_period;
>> + sdata->ctr_values[idx] = init_val;
>> + }
>> + /*
>> + * We do not need to update the non-overflow counters the previous
>> + * value should have been there already.
>> + */
>> + }
>> +
>> + for (idx = 0; idx < BITS_TO_LONGS(RISCV_MAX_COUNTERS); idx++) {
>> + /* Start all the counters in a single shot */
>> + sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_START, idx * BITS_PER_LONG,
>> + cpu_hw_evt->used_hw_ctrs[idx], flag, 0, 0, 0);
>> + }
>> +}
>> +
>> +static void pmu_sbi_start_overflow_mask(struct riscv_pmu *pmu,
>> + unsigned long ctr_ovf_mask)
>> +{
>> + struct cpu_hw_events *cpu_hw_evt = this_cpu_ptr(pmu->hw_events);
>> +
>> + if (sbi_pmu_snapshot_available())
>> + pmu_sbi_start_ovf_ctrs_snapshot(cpu_hw_evt, ctr_ovf_mask);
>> + else
>> + pmu_sbi_start_ovf_ctrs_sbi(cpu_hw_evt, ctr_ovf_mask);
>> +}
>> +
>> static irqreturn_t pmu_sbi_ovf_handler(int irq, void *dev)
>> {
>> struct perf_sample_data data;
>> @@ -716,6 +879,7 @@ static irqreturn_t pmu_sbi_ovf_handler(int irq, void *dev)
>> unsigned long overflowed_ctrs = 0;
>> struct cpu_hw_events *cpu_hw_evt = dev;
>> u64 start_clock = sched_clock();
>> + struct riscv_pmu_snapshot_data *sdata = cpu_hw_evt->snapshot_addr;
>>
>> if (WARN_ON_ONCE(!cpu_hw_evt))
>> return IRQ_NONE;
>> @@ -737,8 +901,10 @@ static irqreturn_t pmu_sbi_ovf_handler(int irq, void *dev)
>> pmu_sbi_stop_hw_ctrs(pmu);
>>
>> /* Overflow status register should only be read after counter are stopped */
>> - ALT_SBI_PMU_OVERFLOW(overflow);
>> -
>> + if (sbi_pmu_snapshot_available())
>> + overflow = sdata->ctr_overflow_mask;
>> + else
>> + ALT_SBI_PMU_OVERFLOW(overflow);
>> /*
>> * Overflow interrupt pending bit should only be cleared after stopping
>> * all the counters to avoid any race condition.
>> @@ -819,6 +985,9 @@ static int pmu_sbi_starting_cpu(unsigned int cpu, struct hlist_node *node)
>> enable_percpu_irq(riscv_pmu_irq, IRQ_TYPE_NONE);
>> }
>>
>> + if (sbi_pmu_snapshot_available())
>> + return pmu_sbi_snapshot_setup(pmu, cpu);
>> +
>> return 0;
>> }
>>
>> @@ -831,6 +1000,9 @@ static int pmu_sbi_dying_cpu(unsigned int cpu, struct hlist_node *node)
>> /* Disable all counters access for user mode now */
>> csr_write(CSR_SCOUNTEREN, 0x0);
>>
>> + if (sbi_pmu_snapshot_available())
>> + return pmu_sbi_snapshot_disable();
>> +
>> return 0;
>> }
>>
>> @@ -1106,10 +1278,6 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>> pmu->event_unmapped = pmu_sbi_event_unmapped;
>> pmu->csr_index = pmu_sbi_csr_index;
>>
>> - ret = cpuhp_state_add_instance(CPUHP_AP_PERF_RISCV_STARTING, &pmu->node);
>> - if (ret)
>> - return ret;
>> -
>> ret = riscv_pm_pmu_register(pmu);
>> if (ret)
>> goto out_unregister;
>> @@ -1118,8 +1286,32 @@ static int pmu_sbi_device_probe(struct platform_device *pdev)
>> if (ret)
>> goto out_unregister;
>>
>> + /* SBI PMU Snapsphot is only available in SBI v2.0 */
>> + if (sbi_v2_available) {
>> + ret = pmu_sbi_snapshot_alloc(pmu);
>> + if (ret)
>> + goto out_unregister;
>> +
>> + ret = pmu_sbi_snapshot_setup(pmu, smp_processor_id());
>> + if (!ret) {
>> + pr_info("SBI PMU snapshot detected\n");
>> + /*
>> + * We enable it once here for the boot cpu. If snapshot shmem setup
>> + * fails during cpu hotplug process, it will fail to start the cpu
>> + * as we can not handle hetergenous PMUs with different snapshot
>> + * capability.
>> + */
>> + static_branch_enable(&sbi_pmu_snapshot_available);
>> + }
>> + /* Snapshot is an optional feature. Continue if not available */
>> + }
>> +
>> register_sysctl("kernel", sbi_pmu_sysctl_table);
>>
>> + ret = cpuhp_state_add_instance(CPUHP_AP_PERF_RISCV_STARTING, &pmu->node);
>> + if (ret)
>> + return ret;
>
> This should be goto out_unregister, and in the case of sbi_v2_available we
> also need a pmu_sbi_snapshot_free() and a pmu_sbi_snapshot_disable().
>

Yes. Thanks for catching it. Fixed

>> +
>> return 0;
>>
>> out_unregister:
>> diff --git a/include/linux/perf/riscv_pmu.h b/include/linux/perf/riscv_pmu.h
>> index 43282e22ebe1..c3fa90970042 100644
>> --- a/include/linux/perf/riscv_pmu.h
>> +++ b/include/linux/perf/riscv_pmu.h
>> @@ -39,6 +39,12 @@ struct cpu_hw_events {
>> DECLARE_BITMAP(used_hw_ctrs, RISCV_MAX_COUNTERS);
>> /* currently enabled firmware counters */
>> DECLARE_BITMAP(used_fw_ctrs, RISCV_MAX_COUNTERS);
>> + /* The virtual address of the shared memory where counter snapshot will be taken */
>> + void *snapshot_addr;
>> + /* The physical address of the shared memory where counter snapshot will be taken */
>> + phys_addr_t snapshot_addr_phys;
>> + /* Boolean flag to indicate setup is already done */
>> + bool snapshot_set_done;
>> };
>>
>> struct riscv_pmu {
>> --
>> 2.34.1
>>
>
> Thanks,
> drew