On Tue, Oct 06, 2015 at 01:49:26PM -0400, Christopher Covington wrote:
> Check the numbers of cycles per instruction (CPI) implied by ARM PMU
> cycle counter values. Check that in -icount mode these strictly
> match the specified rate.
>
> Signed-off-by: Christopher Covington <cov@xxxxxxxxxxxxxx>
> ---
> arm/pmu.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> arm/unittests.cfg | 13 ++++++++++
> 2 files changed, 84 insertions(+), 1 deletion(-)
>
> diff --git a/arm/pmu.c b/arm/pmu.c
> index 589e605..0ad113d 100644
> --- a/arm/pmu.c
> +++ b/arm/pmu.c
> @@ -84,12 +84,82 @@ 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, struct pmu_data pmcr)
> +{
> + int i = (num - 1) / 2;
> +
> + if (num < 3 || ((num - 1) % 2))
> + abort();
assert(num >= 3 && ((num - 1) % 2) == 0);
> +
> + asm volatile(
> + "msr pmcr_el0, %[pmcr]\n"
^\t
> + "1: subs %[i], %[i], #1\n"
^\t ^\t
> + "b.gt 1b\n"
^\t
> + "msr pmcr_el0, xzr"
^\t
> + : [i] "+r" (i) : [pmcr] "r" (pmcr) : "cc");
> +}
> +
> +/* 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 pmcr;
> +
> + pmcr.cycle_counter_reset = 1;
> + pmcr.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 < samples; j++) {
> + int cycles;
> +
> + measure_instrs(i, pmcr);
> + asm volatile("mrs %0, pmccntr_el0" : "=r" (cycles));
> + printf(" %d", cycles);
> +
> + if (!cycles || (cpi > 0 && cycles != i * cpi)) {
> + printf("\n");
> + return false;
> + }
> +
> + sum += cycles;
> + }
> + avg = sum / samples;
> + printf(" sum=%d avg=%d avg_ipc=%d avg_cpi=%d\n",
> + sum, avg, i / avg, avg / i);
> + }
> +
> + return true;
> +}
> +
> +int main(int argc, char *argv[])
> {
> report_prefix_push("pmu");
>
> report("Control register", check_pmcr());
> report("Monotonically increasing cycle count", check_cycles_increase());
>
> + int cpi = (argc == 1 ? atol(argv[0]) : 0);
I prefer variable declarations at the top of the function, and
int cpi = 0;
if (argc > 1)
cpi = atol(argv[0]);
looks a bit better to me.
> +
> + report("Cycle/instruction ratio", check_cpi(cpi));
> +
> return report_summary();
> }
> diff --git a/arm/unittests.cfg b/arm/unittests.cfg
> index fd94adb..333ee0d 100644
> --- a/arm/unittests.cfg
> +++ b/arm/unittests.cfg
> @@ -39,4 +39,17 @@ groups = selftest
> # Test PMU support without -icount
> [pmu]
> file = pmu.flat
> +extra_params = -append '-1'
Why do we need this cpu == -1? Can't it just be zero?
> +groups = pmu
> +
> +# Test PMU support with -icount IPC=1
> +[pmu-icount-1]
> +file = pmu.flat
> +extra_params = -icount 0 -append '1'
> +groups = pmu
> +
> +# Test PMU support with -icount IPC=256
> +[pmu-icount-256]
> +file = pmu.flat
> +extra_params = -icount 8 -append '256'
> groups = pmu
-icount is a tcg specific parameter. I have a patch[*] in my staging
branch which allows you to specify 'accel = tcg' in unittests.cfg for
this type of test. You'll need to use that for anything with -icount
on the extra_params list.
Thanks,
drew
[*] https://github.com/rhdrjones/kvm-unit-tests/commit/85e084cf263e76484f7d82cbc9add4e7602f80a4
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