[kvm-unit-tests PATCH v1 1/2] lib/s390x: time: add wrapper for stckf

Nico Boehr
2022-08-30T11:56:35Z

Upcoming changes will do performance measurements of instructions. Since
stck is designed to return unique values even on concurrent calls, it is
unsuited for performance measurements. stckf should be used in this
case.

Hence, add a nice wrapper for stckf to the time library.

Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
---
lib/s390x/asm/time.h | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/lib/s390x/asm/time.h b/lib/s390x/asm/time.h
index 7652a151e87a..d7c2bcb4f306 100644
--- a/lib/s390x/asm/time.h
+++ b/lib/s390x/asm/time.h
@@ -14,6 +14,15 @@
#define STCK_SHIFT_US (63 - 51)
#define STCK_MAX ((1UL << 52) - 1)

+static inline uint64_t get_clock_fast(void)
+{
+ uint64_t clk;
+
+ asm volatile(" stckf %0 " : : "Q"(clk) : "memory");
+
+ return clk;
+}
+
static inline uint64_t get_clock_us(void)
{
uint64_t clk;
--
2.36.1