[v2] RISC-V SBI v2.0 PMU improvements and Perf sampling in KVM guest

[v2 06/10] RISC-V: KVM: No need to update the counter value during reset

Posted by Atish Patra 1 year, 12 months ago

The virtual counter value is updated during pmu_ctr_read. There is no need
to update it in reset case. Otherwise, it will be counted twice which is
incorrect.

Fixes: 0cb74b65d2e5 ("RISC-V: KVM: Implement perf support without sampling")
Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 arch/riscv/kvm/vcpu_pmu.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
index 86391a5061dd..8c44f26e754d 100644
--- a/arch/riscv/kvm/vcpu_pmu.c
+++ b/arch/riscv/kvm/vcpu_pmu.c
@@ -432,12 +432,9 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
 				sbiret = SBI_ERR_ALREADY_STOPPED;
 			}
 
-			if (flags & SBI_PMU_STOP_FLAG_RESET) {
-				/* Relase the counter if this is a reset request */
-				pmc->counter_val += perf_event_read_value(pmc->perf_event,
-									  &enabled, &running);
+			if (flags & SBI_PMU_STOP_FLAG_RESET)
+				/* Release the counter if this is a reset request */
 				kvm_pmu_release_perf_event(pmc);
-			}
 		} else {
 			sbiret = SBI_ERR_INVALID_PARAM;
 		}
-- 
2.34.1

Re: [v2 06/10] RISC-V: KVM: No need to update the counter value during reset

Posted by Anup Patel 1 year, 12 months ago

On Sat, Dec 30, 2023 at 3:20 AM Atish Patra <atishp@rivosinc.com> wrote:
>
> The virtual counter value is updated during pmu_ctr_read. There is no need
> to update it in reset case. Otherwise, it will be counted twice which is
> incorrect.
>
> Fixes: 0cb74b65d2e5 ("RISC-V: KVM: Implement perf support without sampling")
> Signed-off-by: Atish Patra <atishp@rivosinc.com>

LGTM.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
>  arch/riscv/kvm/vcpu_pmu.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index 86391a5061dd..8c44f26e754d 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -432,12 +432,9 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
>                                 sbiret = SBI_ERR_ALREADY_STOPPED;
>                         }
>
> -                       if (flags & SBI_PMU_STOP_FLAG_RESET) {
> -                               /* Relase the counter if this is a reset request */
> -                               pmc->counter_val += perf_event_read_value(pmc->perf_event,
> -                                                                         &enabled, &running);
> +                       if (flags & SBI_PMU_STOP_FLAG_RESET)
> +                               /* Release the counter if this is a reset request */
>                                 kvm_pmu_release_perf_event(pmc);
> -                       }
>                 } else {
>                         sbiret = SBI_ERR_INVALID_PARAM;
>                 }
> --
> 2.34.1
>