[PATCH v4] arch/powerpc/kvm: Add support for reading VPA counters for pseries guests
Madhavan Srinivasan
maddy at linux.ibm.com
Thu Mar 28 00:07:04 AEDT 2024
On 3/26/24 3:10 PM, Gautam Menghani wrote:
> PAPR hypervisor has introduced three new counters in the VPA area of
> LPAR CPUs for KVM L2 guest (see [1] for terminology) observability - 2
> for context switches from host to guest and vice versa, and 1 counter
> for getting the total time spent inside the KVM guest. Add a tracepoint
> that enables reading the counters for use by ftrace/perf. Note that this
> tracepoint is only available for nestedv2 API (i.e, KVM on PowerVM).
>
> Also maintain an aggregation of the context switch times in vcpu->arch.
> This will be useful in getting the aggregate times with a pmu driver
> which will be upstreamed in the near future.
>
> [1] Terminology:
> a. L1 refers to the VM (LPAR) booted on top of PAPR hypervisor
> b. L2 refers to the KVM guest booted on top of L1.
>
> Signed-off-by: Vaibhav Jain<vaibhav at linux.ibm.com>
> Signed-off-by: Gautam Menghani<gautam at linux.ibm.com>
> ---
> v1 -> v2:
> 1. Fix the build error due to invalid struct member reference.
>
> v2 -> v3:
> 1. Move the counter disabling and zeroing code to a different function.
> 2. Move the get_lppaca() inside the tracepoint_enabled() branch.
> 3. Add the aggregation logic to maintain total context switch time.
>
> v3 -> v4:
> 1. After vcpu_run, check the VPA flag instead of checking for tracepoint
> being enabled for disabling the cs time accumulation.
>
> arch/powerpc/include/asm/kvm_host.h | 5 +++++
> arch/powerpc/include/asm/lppaca.h | 11 ++++++++---
> arch/powerpc/kvm/book3s_hv.c | 30 +++++++++++++++++++++++++++++
> arch/powerpc/kvm/trace_hv.h | 25 ++++++++++++++++++++++++
> 4 files changed, 68 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index 8abac5321..d953b32dd 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -847,6 +847,11 @@ struct kvm_vcpu_arch {
> gpa_t nested_io_gpr;
> /* For nested APIv2 guests*/
> struct kvmhv_nestedv2_io nestedv2_io;
> +
> + /* Aggregate context switch and guest run time info (in ns) */
> + u64 l1_to_l2_cs_agg;
> + u64 l2_to_l1_cs_agg;
> + u64 l2_runtime_agg;
> #endif
>
> #ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
> diff --git a/arch/powerpc/include/asm/lppaca.h b/arch/powerpc/include/asm/lppaca.h
> index 61ec2447d..bda6b86b9 100644
> --- a/arch/powerpc/include/asm/lppaca.h
> +++ b/arch/powerpc/include/asm/lppaca.h
> @@ -62,7 +62,8 @@ struct lppaca {
> u8 donate_dedicated_cpu; /* Donate dedicated CPU cycles */
> u8 fpregs_in_use;
> u8 pmcregs_in_use;
> - u8 reserved8[28];
> + u8 l2_accumul_cntrs_enable; /* Enable usage of counters for KVM guest */
> + u8 reserved8[27];
> __be64 wait_state_cycles; /* Wait cycles for this proc */
> u8 reserved9[28];
> __be16 slb_count; /* # of SLBs to maintain */
> @@ -92,9 +93,13 @@ struct lppaca {
> /* cacheline 4-5 */
>
> __be32 page_ins; /* CMO Hint - # page ins by OS */
> - u8 reserved12[148];
> + u8 reserved12[28];
> + volatile __be64 l1_to_l2_cs_tb;
> + volatile __be64 l2_to_l1_cs_tb;
> + volatile __be64 l2_runtime_tb;
> + u8 reserved13[96];
> volatile __be64 dtl_idx; /* Dispatch Trace Log head index */
> - u8 reserved13[96];
> + u8 reserved14[96];
> } ____cacheline_aligned;
>
> #define lppaca_of(cpu) (*paca_ptrs[cpu]->lppaca_ptr)
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 8e86eb577..dcd6edd3b 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -4108,6 +4108,27 @@ static void vcpu_vpa_increment_dispatch(struct kvm_vcpu *vcpu)
> }
> }
>
> +static void do_trace_nested_cs_time(struct kvm_vcpu *vcpu)
> +{
> + struct lppaca *lp = get_lppaca();
> + u64 l1_to_l2_ns, l2_to_l1_ns, l2_runtime_ns;
> +
> + l1_to_l2_ns = tb_to_ns(be64_to_cpu(lp->l1_to_l2_cs_tb));
> + l2_to_l1_ns = tb_to_ns(be64_to_cpu(lp->l2_to_l1_cs_tb));
> + l2_runtime_ns = tb_to_ns(be64_to_cpu(lp->l2_runtime_tb));
> + trace_kvmppc_vcpu_exit_cs_time(vcpu, l1_to_l2_ns, l2_to_l1_ns,
> + l2_runtime_ns);
> + lp->l1_to_l2_cs_tb = 0;
> + lp->l2_to_l1_cs_tb = 0;
> + lp->l2_runtime_tb = 0;
> + lp->l2_accumul_cntrs_enable = 0;
> +
> + // Maintain an aggregate of context switch times
> + vcpu->arch.l1_to_l2_cs_agg += l1_to_l2_ns;
> + vcpu->arch.l2_to_l1_cs_agg += l2_to_l1_ns;
> + vcpu->arch.l2_runtime_agg += l2_runtime_ns;
> +}
> +
> static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
> unsigned long lpcr, u64 *tb)
> {
> @@ -4130,6 +4151,11 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
> kvmppc_gse_put_u64(io->vcpu_run_input, KVMPPC_GSID_LPCR, lpcr);
>
> accumulate_time(vcpu, &vcpu->arch.in_guest);
> +
> + /* Enable the guest host context switch time tracking */
> + if (unlikely(trace_kvmppc_vcpu_exit_cs_time_enabled()))
> + get_lppaca()->l2_accumul_cntrs_enable = 1;
can we wrap "get_lppaca()->l2_accumul_cntrs_enable" under wrapper function
like is_l2_accumul_cntrs_enable(), set_l2_accumul_cntrs_enable() and
unset_l2_accumul_cntrs_enable()?
set/unset does not need a parameter and in future incase if we want to
check and set or check and unset, we could have additional code in there.
Maddy
> +
> rc = plpar_guest_run_vcpu(0, vcpu->kvm->arch.lpid, vcpu->vcpu_id,
> &trap, &i);
>
> @@ -4156,6 +4182,10 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu *vcpu, u64 time_limit,
>
> timer_rearm_host_dec(*tb);
>
> + /* Record context switch and guest_run_time data */
> + if (get_lppaca()->l2_accumul_cntrs_enable)
> + do_trace_nested_cs_time(vcpu);
> +
> return trap;
> }
>
> diff --git a/arch/powerpc/kvm/trace_hv.h b/arch/powerpc/kvm/trace_hv.h
> index 8d57c8428..ab19977c9 100644
> --- a/arch/powerpc/kvm/trace_hv.h
> +++ b/arch/powerpc/kvm/trace_hv.h
> @@ -491,6 +491,31 @@ TRACE_EVENT(kvmppc_run_vcpu_enter,
> TP_printk("VCPU %d: tgid=%d", __entry->vcpu_id, __entry->tgid)
> );
>
> +TRACE_EVENT(kvmppc_vcpu_exit_cs_time,
> + TP_PROTO(struct kvm_vcpu *vcpu, u64 l1_to_l2_cs, u64 l2_to_l1_cs,
> + u64 l2_runtime),
> +
> + TP_ARGS(vcpu, l1_to_l2_cs, l2_to_l1_cs, l2_runtime),
> +
> + TP_STRUCT__entry(
> + __field(int, vcpu_id)
> + __field(__u64, l1_to_l2_cs_ns)
> + __field(__u64, l2_to_l1_cs_ns)
> + __field(__u64, l2_runtime_ns)
> + ),
> +
> + TP_fast_assign(
> + __entry->vcpu_id = vcpu->vcpu_id;
> + __entry->l1_to_l2_cs_ns = l1_to_l2_cs;
> + __entry->l2_to_l1_cs_ns = l2_to_l1_cs;
> + __entry->l2_runtime_ns = l2_runtime;
> + ),
> +
> + TP_printk("VCPU %d: l1_to_l2_cs_time=%llu-ns l2_to_l1_cs_time=%llu-ns l2_runtime=%llu-ns",
> + __entry->vcpu_id, __entry->l1_to_l2_cs_ns,
> + __entry->l2_to_l1_cs_ns, __entry->l2_runtime_ns)
> +);
> +
> TRACE_EVENT(kvmppc_run_vcpu_exit,
> TP_PROTO(struct kvm_vcpu *vcpu),
>
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