Calculate the numbers of cycles per instruction (CPI) implied by ARM
PMU cycle counter values.
Signed-off-by: Christopher Covington <cov@xxxxxxxxxxxxxx>
---
arm/pmu.c | 109 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 108 insertions(+), 1 deletion(-)
diff --git a/arm/pmu.c b/arm/pmu.c
index 65b7df1..ca00422 100644
--- a/arm/pmu.c
+++ b/arm/pmu.c
@@ -62,6 +62,23 @@ static inline void disable_counter(uint32_t idx)
{
asm volatile("mrc p15, 0, %0, c9, c12, 1" : : "r" (1 << idx));
}
+
+/*
+ * Extra instructions inserted by the compiler would be difficult to compensate
+ * for, so hand assemble everything between, and including, the PMCR accesses
+ * to start and stop counting.
+ */
+static inline void loop(int i, uint32_t pmcr)
+{
+ asm volatile(
+ " mcr p15, 0, %[pmcr], c9, c12, 0\n"
+ "1: subs %[i], %[i], #1\n"
+ " bgt 1b\n"
+ " mcr p15, 0, %[z], c9, c12, 0\n"
+ : [i] "+r" (i)
+ : [pmcr] "r" (pmcr), [z] "r" (0)
+ : "cc");
+}
#elif defined(__aarch64__)
static inline uint32_t get_pmcr(void)
{
@@ -98,6 +115,23 @@ static inline void disable_counter(uint32_t idx)
{
asm volatile("msr pmcntensclr_el0, %0" : : "r" (1 << idx));
}
+
+/*
+ * Extra instructions inserted by the compiler would be difficult to compensate
+ * for, so hand assemble everything between, and including, the PMCR accesses
+ * to start and stop counting.
+ */
+static inline void loop(int i, uint32_t pmcr)
+{
+ asm volatile(
+ " msr pmcr_el0, %[pmcr]\n"
+ "1: subs %[i], %[i], #1\n"
+ " b.gt 1b\n"
+ " msr pmcr_el0, xzr\n"
+ : [i] "+r" (i)
+ : [pmcr] "r" (pmcr)
+ : "cc");
+}
#endif
struct pmu_data {
@@ -171,12 +205,85 @@ static bool check_cycles_increase(void)
return true;
}
-int main(void)
+/*
+ * Execute a known number of guest instructions. Only odd instruction counts
+ * greater than or equal to 3 are supported by the in-line assembly code. The
+ * control register (PMCR_EL0) is initialized with the provided value (allowing
+ * for example for the cycle counter or event counters to be reset). At the end
+ * of the exact instruction loop, zero is written to PMCR_EL0 to disable
+ * counting, allowing the cycle counter or event counters to be read at the
+ * leisure of the calling code.
+ */
+static void measure_instrs(int num, uint32_t pmcr)
+{
+ int i = (num - 1) / 2;
+
+ assert(num >= 3 && ((num - 1) % 2 == 0));
+ loop(i, pmcr);
+}
+
+/*
+ * Measure cycle counts for various known instruction counts. Ensure that the
+ * cycle counter progresses (similar to check_cycles_increase() but with more
+ * instructions and using reset and stop controls). If supplied a positive,
+ * nonzero CPI parameter, also strictly check that every measurement matches
+ * it. Strict CPI checking is used to test -icount mode.
+ */
+static bool check_cpi(int cpi)
+{
+ struct pmu_data pmu = {{0}};
+
+ enable_counter(ARMV8_PMU_CYCLE_IDX);
+ set_pmccfiltr(0); /* count cycles in EL0, EL1, but not EL2 */
+
+ pmu.cycle_counter_reset = 1;
+ pmu.enable = 1;
+
+ if (cpi > 0)
+ printf("Checking for CPI=%d.\n", cpi);
+ printf("instrs : cycles0 cycles1 ...\n");
+
+ for (int i = 3; i < 300; i += 32) {
+ int avg, sum = 0;
+
+ printf("%d :", i);
+ for (int j = 0; j < NR_SAMPLES; j++) {
+ int cycles;
+
+ measure_instrs(i, pmu.pmcr_el0);
+ cycles = get_pmccntr();
+ printf(" %d", cycles);
+
+ if (!cycles || (cpi > 0 && cycles != i * cpi)) {
+ printf("\n");
+ return false;
+ }
+
+ sum += cycles;
+ }
+ avg = sum / NR_SAMPLES;
+ printf(" sum=%d avg=%d avg_ipc=%d avg_cpi=%d\n",
+ sum, avg, i / avg, avg / i);
+ }
+
+ pmu.enable = 0;
+ set_pmcr(pmu.pmcr_el0);
+
+ return true;
+}
+
+int main(int argc, char *argv[])
{
+ int cpi = 0;
+
+ if (argc >= 1)
+ cpi = atol(argv[0]);
+
report_prefix_push("pmu");
report("Control register", check_pmcr());
report("Monotonically increasing cycle count", check_cycles_increase());
+ report("Cycle/instruction ratio", check_cpi(cpi));
return report_summary();
}
--
1.8.3.1
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
