Re: [PATCH v6 08/24] drivers/perf: riscv: Implement SBI PMU snapshot function

[Atish Patra]

On 4/15/24 06:15, Andrew Jones wrote:
> On Wed, Apr 10, 2024 at 05:07:36PM -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@xxxxxxxxxxxx>
> > Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
> > Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> > Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> > ---
> >   drivers/perf/riscv_pmu.c       |   1 +
> >   drivers/perf/riscv_pmu_sbi.c   | 224 +++++++++++++++++++++++++++++++--
> >   include/linux/perf/riscv_pmu.h |   6 +
> >   3 files changed, 219 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
> > index b4efdddb2ad9..36d348753d05 100644
> > --- a/drivers/perf/riscv_pmu.c
> > +++ b/drivers/perf/riscv_pmu.c
> > @@ -408,6 +408,7 @@ 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 f23501898657..e2881415ca0a 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 +511,109 @@ 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);
>
> The SBI_SHMEM_DISABLE patch got moved in front of this patch, but looks
> like it was forgotten to apply it.

Oops. My bad. Fixed it.

> Otherwise,
>
> Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
>
> Thanks,
> drew
>
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