[PATCH v2 1/2] KVM: selftests: Provide generic way to read system counter

[Colton Lewis <coltonlewis@xxxxxxxxxx>]

Provide a generic function to read the system counter from the guest
for timing purposes. A common and important way to measure guest
performance is to measure the amount of time different actions take in
the guest. Provide also a mathematical conversion from cycles to
nanoseconds and a macro for timing individual statements.

Substitute the previous custom implementation of a similar function in
system_counter_offset_test with this new implementation.

Signed-off-by: Colton Lewis <coltonlewis@xxxxxxxxxx>
---
 .../testing/selftests/kvm/include/kvm_util.h  | 15 ++++++++++
 tools/testing/selftests/kvm/lib/kvm_util.c    | 30 +++++++++++++++++++
 .../kvm/system_counter_offset_test.c          | 10 ++-----
 3 files changed, 47 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index c9286811a4cb..8b478eabee4c 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -10,4 +10,19 @@
 #include "kvm_util_base.h"
 #include "ucall_common.h"

+#if defined(__aarch64__) || defined(__x86_64__)
+
+uint64_t cycles_read(void);
+double cycles_to_ns(struct kvm_vcpu *vcpu, double cycles);
+
+#define MEASURE_CYCLES(x)			\
+	({					\
+		uint64_t start;			\
+		start = cycles_read();		\
+		x;				\
+		cycles_read() - start;		\
+	})
+
+#endif
+
 #endif /* SELFTEST_KVM_UTIL_H */
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 3ea24a5f4c43..780481a92efe 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -2135,3 +2135,34 @@ void __attribute((constructor)) kvm_selftest_init(void)

 	kvm_selftest_arch_init();
 }
+
+#if defined(__aarch64__)
+
+#include "arch_timer.h"
+
+uint64_t cycles_read(void)
+{
+	return timer_get_cntct(VIRTUAL);
+}
+
+double cycles_to_ns(struct kvm_vcpu *vcpu, double cycles)
+{
+	return cycles * (1e9 / timer_get_cntfrq());
+}
+
+#elif defined(__x86_64__)
+
+#include "processor.h"
+
+uint64_t cycles_read(void)
+{
+	return rdtsc();
+}
+
+double cycles_to_ns(struct kvm_vcpu *vcpu, double cycles)
+{
+	uint64_t tsc_khz = __vcpu_ioctl(vcpu, KVM_GET_TSC_KHZ, NULL);
+
+	return cycles * (1e9 / (tsc_khz * 1000));
+}
+#endif
diff --git a/tools/testing/selftests/kvm/system_counter_offset_test.c b/tools/testing/selftests/kvm/system_counter_offset_test.c
index 7f5b330b6a1b..44101d0fcb48 100644
--- a/tools/testing/selftests/kvm/system_counter_offset_test.c
+++ b/tools/testing/selftests/kvm/system_counter_offset_test.c
@@ -39,14 +39,9 @@ static void setup_system_counter(struct kvm_vcpu *vcpu, struct test_case *test)
 			     &test->tsc_offset);
 }

-static uint64_t guest_read_system_counter(struct test_case *test)
-{
-	return rdtsc();
-}
-
 static uint64_t host_read_guest_system_counter(struct test_case *test)
 {
-	return rdtsc() + test->tsc_offset;
+	return cycles_read() + test->tsc_offset;
 }

 #else /* __x86_64__ */
@@ -63,9 +58,8 @@ static void guest_main(void)
 	int i;

 	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
-		struct test_case *test = &test_cases[i];

-		GUEST_SYNC_CLOCK(i, guest_read_system_counter(test));
+		GUEST_SYNC_CLOCK(i, cycles_read());
 	}
 }

--
2.40.0.rc1.284.g88254d51c5-goog