Re: [PATCH] arch/powerpc/kvm: Add support for reading VPA counters for pseries guests
On Wed Mar 20, 2024 at 12:28 AM AEST, 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).
>
> [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
> Signed-off-by: Gautam Menghani
> ---
> arch/powerpc/include/asm/kvm_host.h | 5 +
> arch/powerpc/include/asm/lppaca.h | 11 ---
> arch/powerpc/kvm/book3s_hv.c| 20
> arch/powerpc/kvm/trace_hv.h | 24
> 4 files changed, 57 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_host.h
> b/arch/powerpc/include/asm/kvm_host.h
> index 8abac5321..26d7bb4b9 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;
> +
> + /* For VPA counters having context switch and guest run time info (in
> ns) */
> + u64 l1_to_l2_cs;
> + u64 l2_to_l1_cs;
> + u64 l2_runtime;
> #endif
>
> #ifdef CONFIG_KVM_BOOK3S_HV_EXIT_TIMING
These aren't required here if it's just used for tracing over
a single run vcpu call are they?
> 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 2b04eba90..b94461b5f 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -4092,6 +4092,7 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu
> *vcpu, u64 time_limit,
> unsigned long msr, i;
> int trap;
> long rc;
> + struct lppaca *lp = get_lppaca();
Does get_lppaca() emit some inline asm that can't be optimised?
Could move it under the unlikely branches if so.
>
> io = >arch.nestedv2_io;
>
KVM L0 could in theory provide this for v1 L1s too, so could this
be done at a higher level to cover both?
> @@ -4107,6 +4108,17 @@ 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, >arch.in_guest);
> +
> + /* Reset the guest host context switch timing */
> + if (unlikely(trace_kvmppc_vcpu_exit_cs_time_enabled())) {
> + lp->l2_accumul_cntrs_enable = 1;
> + lp->l1_to_l2_cs_tb = 0;
> + lp->l2_to_l1_cs_tb = 0;
> + lp->l2_runtime_tb = 0;
> + } else {
> + lp->l2_accumul_cntrs_enable = 0;
> + }
Instead of zeroing here zero after the exit, which avoids the
else branch and possibly avoids an obscure race with the counters.
What if trace_kvmppc_vcpu_exit_cs_time_enabled() is false here...
> +
> rc = plpar_guest_run_vcpu(0, vcpu->kvm->arch.lpid, vcpu->vcpu_id,
> , );
>
> @@ -4133,6 +4145,14 @@ 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 (unlikely(trace_kvmppc_vcpu_exit_cs_time_enabled())) {
> + vcpu->arch.l1_to_l2_cs =
> tb_to_ns(be64_to_cpu(lp->l1_to_l2_cs_tb));
> + vcpu->arch.l2_to_l1_cs =
>
[PATCH] arch/powerpc/kvm: Add support for reading VPA counters for pseries guests
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).
[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
Signed-off-by: Gautam Menghani
---
arch/powerpc/include/asm/kvm_host.h | 5 +
arch/powerpc/include/asm/lppaca.h | 11 ---
arch/powerpc/kvm/book3s_hv.c| 20
arch/powerpc/kvm/trace_hv.h | 24
4 files changed, 57 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/include/asm/kvm_host.h
b/arch/powerpc/include/asm/kvm_host.h
index 8abac5321..26d7bb4b9 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;
+
+ /* For VPA counters having context switch and guest run time info (in
ns) */
+ u64 l1_to_l2_cs;
+ u64 l2_to_l1_cs;
+ u64 l2_runtime;
#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 2b04eba90..b94461b5f 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4092,6 +4092,7 @@ static int kvmhv_vcpu_entry_nestedv2(struct kvm_vcpu
*vcpu, u64 time_limit,
unsigned long msr, i;
int trap;
long rc;
+ struct lppaca *lp = get_lppaca();
io = >arch.nestedv2_io;
@@ -4107,6 +4108,17 @@ 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, >arch.in_guest);
+
+ /* Reset the guest host context switch timing */
+ if (unlikely(trace_kvmppc_vcpu_exit_cs_time_enabled())) {
+ lp->l2_accumul_cntrs_enable = 1;
+ lp->l1_to_l2_cs_tb = 0;
+ lp->l2_to_l1_cs_tb = 0;
+ lp->l2_runtime_tb = 0;
+ } else {
+ lp->l2_accumul_cntrs_enable = 0;
+ }
+
rc = plpar_guest_run_vcpu(0, vcpu->kvm->arch.lpid, vcpu->vcpu_id,
, );
@@ -4133,6 +4145,14 @@ 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 (unlikely(trace_kvmppc_vcpu_exit_cs_time_enabled())) {
+ vcpu->arch.l1_to_l2_cs =
tb_to_ns(be64_to_cpu(lp->l1_to_l2_cs_tb));
+ vcpu->arch.l2_to_l1_cs =
tb_to_ns(be64_to_cpu(lp->l2_to_l1_cs_tb));
+ vcpu->arch.l2_runtime =
tb_to_ns(be64_to_cpu(lp->l2_runtime_tb));
+ trace_kvmppc_vcpu_exit_cs_time(vcpu);
+ }
+
return trap;
}
diff --git a/arch/powerpc/kvm/trace_hv.h b/arch/powerpc/kvm/trace_hv.h
index 8d57c8428..10b8f6e5a 100644
--- a/arch/powerpc/kvm/trace_hv.h
+++ b/arch/powerpc/kvm/trace_hv.h
@@ -491,6 +491,30 @@ 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),
+
+ TP_ARGS(vcpu),
+
+ TP_STRUCT__entry(
+ __field(int,vcpu_id)
+ __field(__u64,
