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

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Message-ID: <dd14fc53-deda-4086-aac0-2dde7f065bb0@rivosinc.com>
Date: Tue, 16 Apr 2024 01:33:22 -0700
From: Atish Patra <atishp@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: linux-kernel@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>,
 Anup Patel <anup@...infault.org>, Conor Dooley <conor.dooley@...rochip.com>,
 Ajay Kaher <ajay.kaher@...adcom.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alexghiti@...osinc.com>,
 Alexey Makhalov <alexey.amakhalov@...adcom.com>,
 Atish Patra <atishp@...shpatra.org>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Juergen Gross <jgross@...e.com>,
 kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org,
 Mark Rutland <mark.rutland@....com>, Palmer Dabbelt <palmer@...belt.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Paul Walmsley
 <paul.walmsley@...ive.com>, Shuah Khan <shuah@...nel.org>,
 virtualization@...ts.linux.dev, Will Deacon <will@...nel.org>, x86@...nel.org
Subject: Re: [PATCH v6 08/24] drivers/perf: riscv: Implement SBI PMU snapshot
 function

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@...osinc.com>
>> Reviewed-by: Anup Patel <anup@...infault.org>
>> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
>> Signed-off-by: Atish Patra <atishp@...osinc.com>
>> ---
>>   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@...tanamicro.com>
> 
> Thanks,
> drew
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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