[kvm-unit-tests 1/1] arm64: microbench: Move the read of the count register and the ISB operation out of the while loop

[heqiong <heqiong1557@xxxxxxxxxxxxxx>]

Reducing the impact of the cntvct_el0 register and isb() operation
on microbenchmark test results to improve testing accuracy and reduce
latency in test results.
---
 arm/micro-bench.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arm/micro-bench.c b/arm/micro-bench.c
index fbe59d03..6b940d56 100644
--- a/arm/micro-bench.c
+++ b/arm/micro-bench.c
@@ -346,17 +346,21 @@ static void loop_test(struct exit_test *test)
 		}
 	}
 
+	dsb(ish);
+	isb();
+	start = read_sysreg(cntpct_el0);
+	isb();
 	while (ntimes < test->times && total_ns.ns < NS_5_SECONDS) {
-		isb();
-		start = read_sysreg(cntvct_el0);
 		test->exec();
-		isb();
-		end = read_sysreg(cntvct_el0);
 
 		ntimes++;
-		total_ticks += (end - start);
-		ticks_to_ns_time(total_ticks, &total_ns);
 	}
+	dsb(ish);
+	isb();
+	end = read_sysreg(cntpct_el0);
+
+	total_ticks = end - start;
+	ticks_to_ns_time(total_ticks, &total_ns);
 
 	if (test->post) {
 		test->post(ntimes, &total_ticks);
-- 
2.31.1