From: Christopher Covington <cov@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Signed-off-by: Wei Huang <wei@xxxxxxxxxx>
---
arm/pmu.c | 111 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
arm/unittests.cfg | 14 +++++++
2 files changed, 124 insertions(+), 1 deletion(-)
diff --git a/arm/pmu.c b/arm/pmu.c
index fa87de4..b36c4fb 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.
+ */
+static inline void loop(int i, uint32_t pmcr)
+{
+ asm volatile(
+ " mcr p15, 0, %[pmcr], c9, c12, 0\n"
+ " isb\n"
+ "1: subs %[i], %[i], #1\n"
+ " bgt 1b\n"
+ " mcr p15, 0, %[z], c9, c12, 0\n"
+ " isb\n"
+ : [i] "+r" (i)
+ : [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.
+ */
+static inline void loop(int i, uint32_t pmcr)
+{
+ asm volatile(
+ " msr pmcr_el0, %[pmcr]\n"
+ " isb\n"
+ "1: subs %[i], %[i], #1\n"
+ " b.gt 1b\n"
+ " msr pmcr_el0, xzr\n"
+ " isb\n"
+ : [i] "+r" (i)
+ : [pmcr] "r" (pmcr)
+ : "cc");
+}
#endif
/*
@@ -204,6 +242,71 @@ 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 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)
+{
+ uint32_t pmcr = pmcr_read() | PMU_PMCR_LC | PMU_PMCR_C | PMU_PMCR_E;
+
+ if (cpi > 0)
+ printf("Checking for CPI=%d.\n", cpi);
+ printf("instrs : cycles0 cycles1 ...\n");
+
+ for (unsigned int i = 3; 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);
+
+ /*
+ * 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.
+ */
+ if (!cycles || (cpi > 0 && cycles != i * cpi) ||
+ (cycles & 0xffffffff00000000)) {
+ printf("\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 +321,19 @@ void pmu_init(void)
pmccfiltr_write(0); /* count cycles in EL0, EL1, but not EL2 */
}
-int main(void)
+int main(int argc, char *argv[])
{
+ int cpi = 0;
+
+ if (argc >= 1)
+ cpi = atol(argv[0]);
+
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 7645180..2050dc8 100644
--- a/arm/unittests.cfg
+++ b/arm/unittests.cfg
@@ -59,3 +59,17 @@ groups = selftest
[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
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