[kvm-unit-tests PATCH v10 3/3] arm: pmu: Add CPI checking

Wei Huang
2016-11-21T20:24:55Z

From: Christopher Covington <cov@codeaurora.org>

Calculate the numbers of cycles per instruction (CPI) implied by ARM
PMU cycle counter values. The code includes a strict checking facility
intended for the -icount option in TCG mode in the configuration file.

Signed-off-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: Wei Huang <wei@redhat.com>
---
arm/pmu.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
arm/unittests.cfg | 14 +++++++
2 files changed, 132 insertions(+), 1 deletion(-)

diff --git a/arm/pmu.c b/arm/pmu.c
index 176b070..129ef1e 100644
--- a/arm/pmu.c
+++ b/arm/pmu.c
@@ -104,6 +104,25 @@ static inline uint32_t id_dfr0_read(void)
asm volatile("mrc p15, 0, %0, c0, c1, 2" : "=r" (val));
return val;
}
+
+/*
+ * 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. Total cycles = isb + mcr + 2*loop = 2 + 2*loop.
+ */
+static inline void precise_cycles_loop(int loop, uint32_t pmcr)
+{
+ asm volatile(
+ " mcr p15, 0, %[pmcr], c9, c12, 0\n"
+ " isb\n"
+ "1: subs %[loop], %[loop], #1\n"
+ " bgt 1b\n"
+ " mcr p15, 0, %[z], c9, c12, 0\n"
+ " isb\n"
+ : [loop] "+r" (loop)
+ : [pmcr] "r" (pmcr), [z] "r" (0)
+ : "cc");
+}
#elif defined(__aarch64__)
static inline uint32_t pmcr_read(void)
{
@@ -150,6 +169,25 @@ static inline uint32_t id_dfr0_read(void)
asm volatile("mrs %0, id_dfr0_el1" : "=r" (id));
return id;
}
+
+/*
+ * 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. Total cycles = isb + msr + 2*loop = 2 + 2*loop.
+ */
+static inline void precise_cycles_loop(int loop, uint32_t pmcr)
+{
+ asm volatile(
+ " msr pmcr_el0, %[pmcr]\n"
+ " isb\n"
+ "1: subs %[loop], %[loop], #1\n"
+ " b.gt 1b\n"
+ " msr pmcr_el0, xzr\n"
+ " isb\n"
+ : [loop] "+r" (loop)
+ : [pmcr] "r" (pmcr)
+ : "cc");
+}
#endif

/*
@@ -208,6 +246,79 @@ static bool check_cycles_increase(void)
return success;
}

+/*
+ * 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 loop = (num - 2) / 2;
+
+ assert(num >= 4 && ((num - 2) % 2 == 0));
+ precise_cycles_loop(loop, 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)
+{
+ uint32_t pmcr = pmcr_read() | PMU_PMCR_LC | PMU_PMCR_C | PMU_PMCR_E;
+
+ /* init before event access, this test only cares about cycle count */
+ pmcntenset_write(1 << PMU_CYCLE_IDX);
+ pmccfiltr_write(0); /* count cycles in EL0, EL1, but not EL2 */
+
+ if (cpi > 0)
+ printf("Checking for CPI=%d.\n", cpi);
+ printf("instrs : cycles0 cycles1 ...\n");
+
+ for (unsigned int i = 4; i < 300; i += 32) {
+ uint64_t avg, sum = 0;
+
+ printf("%d :", i);
+ for (int j = 0; j < NR_SAMPLES; j++) {
+ uint64_t cycles;
+
+ pmccntr_write(0);
+ measure_instrs(i, pmcr);
+ cycles = pmccntr_read();
+ printf(" %"PRId64"", cycles);
+
+ if (!cycles) {
+ printf("\ncycles not incrementing!\n");
+ return false;
+ } else if (cpi > 0 && cycles != i * cpi) {
+ printf("\nunexpected cycle count received!\n");
+ return false;
+ } else if ((cycles >> 32) != 0) {
+ /* The cycles taken by the loop above should
+ * fit in 32 bits easily. We check the upper
+ * 32 bits of the cycle counter to make sure
+ * there is no supprise. */
+ printf("\ncycle count bigger than 32bit!\n");
+ return false;
+ }
+
+ sum += cycles;
+ }
+ avg = sum / NR_SAMPLES;
+ printf(" sum=%"PRId64" avg=%"PRId64" avg_ipc=%"PRId64" "
+ "avg_cpi=%"PRId64"\n", sum, avg, i / avg, avg / i);
+ }
+
+ return true;
+}
+
void pmu_init(void)
{
uint32_t dfr0;
@@ -218,13 +329,19 @@ void pmu_init(void)
printf("PMU version: %d\n", pmu_version);
}

-int main(void)
+int main(int argc, char *argv[])
{
+ int cpi = 0;
+
+ if (argc > 1)
+ cpi = atol(argv[1]);
+
report_prefix_push("pmu");

pmu_init();
report("Control register", check_pmcr());
report("Monotonically increasing cycle count", check_cycles_increase());
+ report("Cycle/instruction ratio", check_cpi(cpi));

return report_summary();
}
diff --git a/arm/unittests.cfg b/arm/unittests.cfg
index 816f494..044d97c 100644
--- a/arm/unittests.cfg
+++ b/arm/unittests.cfg
@@ -63,3 +63,17 @@ groups = pci
[pmu]
file = pmu.flat
groups = pmu
+
+# Test PMU support (TCG) with -icount IPC=1
+[pmu-tcg-icount-1]
+file = pmu.flat
+extra_params = -icount 0 -append '1'
+groups = pmu
+accel = tcg
+
+# Test PMU support (TCG) with -icount IPC=256
+[pmu-tcg-icount-256]
+file = pmu.flat
+extra_params = -icount 8 -append '256'
+groups = pmu
+accel = tcg
--
1.8.3.1