[PATCH v2 2/2] s390/kvm: Add tracepoint for DIAG 9c directed yield operations

[Ciunas Bennett <ciunas@linux.ibm.com>]

Add a new tracepoint kvm_s390_diag_9c to provide detailed observability
for directed yield operations. The tracepoint captures:
- Source and target VCPU IDs
- Current and target physical CPU numbers
- Operation result (done, ignored, yield forwarded)

This enables better analysis of VCPU scheduling behaviour and helps
diagnose performance issues related to directed yields in virtualised
s390 environments.

Signed-off-by: Ciunas Bennett <ciunas@linux.ibm.com>
---
 arch/s390/kvm/diag.c  |  1 +
 arch/s390/kvm/trace.h | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index 85c84421b510..031ab6e5d6c4 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -228,6 +228,7 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
 out:
 	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: %s", tid,
 		   result);
+	trace_kvm_s390_diag_9c(vcpu, tid, tcpu_cpu, result);
 	return 0;
 }
 
diff --git a/arch/s390/kvm/trace.h b/arch/s390/kvm/trace.h
index aa419eb6a0c8..2d6da21f590c 100644
--- a/arch/s390/kvm/trace.h
+++ b/arch/s390/kvm/trace.h
@@ -283,6 +283,36 @@ TRACE_EVENT(kvm_s390_handle_diag,
 			   __print_symbolic(__entry->code, diagnose_codes))
 	);
 
+TRACE_EVENT(kvm_s390_diag_9c,
+	    TP_PROTO(VCPU_PROTO_COMMON, int target_vcpu, int target_cpu,
+		     const char *result),
+	    TP_ARGS(VCPU_ARGS_COMMON, target_vcpu, target_cpu, result),
+
+	    TP_STRUCT__entry(
+		    VCPU_FIELD_COMMON
+		    __field(int, target_vcpu)
+		    __field(int, target_cpu)
+		    __field(int, current_cpu)
+		    __string(result, result)
+		    ),
+
+	    TP_fast_assign(
+		    VCPU_ASSIGN_COMMON
+		    __entry->target_vcpu = target_vcpu;
+		    __entry->target_cpu = target_cpu;
+		    __entry->current_cpu = smp_processor_id();
+		    __assign_str(result);
+		    ),
+
+	    VCPU_TP_PRINTK(
+		       "diag=9c vcpu=%d pcpu=%d target_vcpu=%d target_pcpu=%d result=%s",
+		       __entry->id,
+		       __entry->current_cpu,
+		       __entry->target_vcpu,
+		       __entry->target_cpu,
+		       __get_str(result))
+	);
+
 TRACE_EVENT(kvm_s390_handle_lctl,
 	    TP_PROTO(VCPU_PROTO_COMMON, int g, int reg1, int reg3, u64 addr),
 	    TP_ARGS(VCPU_ARGS_COMMON, g, reg1, reg3, addr),
-- 
2.54.0