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Message-ID: <20161121094115.j6kqkhubzabclfm2@kamzik.brq.redhat.com>
Date: Mon, 21 Nov 2016 10:41:15 +0100
From: Andrew Jones <drjones@...hat.com>
To: Wei Huang <wei@...hat.com>
Cc: kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
shannon.zhao@...aro.org, kvm@...r.kernel.org, marc.zyngier@....com,
christoffer.dall@...aro.org, cov@...eaurora.org,
will.deacon@....com, mark.rutland@....com, catalin.marinas@....com,
linux-kernel@...r.kernel.org
Subject: Re: [kvm-unit-tests PATCH v9 3/3] arm: pmu: Add CPI checking
On Fri, Nov 18, 2016 at 10:15:42PM -0600, Wei Huang wrote:
> From: Christopher Covington <cov@...eaurora.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@...eaurora.org>
> Signed-off-by: Wei Huang <wei@...hat.com>
> ---
> 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)
Thought you were going to rename this function.
> +{
> + 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)) {
(cycles >> 32) != 0 would look better.
> + printf("\n");
We have 3 cases where we return false here. How about doing the tests
separately and adding descriptive print statements for each?
if (!cycles) {
printf("\ncycles not incrementing!\n");
return false;
} else if (cpi > 0 && cycles != i * cpi) {
...
} else if ((cycles >> 32) != 0) {
...
}
> + 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)
^ this '=' shouldn't be here
> + cpi = atol(argv[0]);
^ sigh, this is still zero...
Looks like you forgot all my comments from the last review round...
> +
> 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
>
drew
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