Re: [PATCH v2] x86: add HPET counter read micro benchmark and enable/disable torture tests

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 14 Jul 2025 16:50:55 +0200
Igor Mammedov <imammedo@redhat.com> wrote:

> test is to be used for benchmarking/validating HPET main counter reading

ignore this one as well, I've just sent v3 with a few fixes

> 
> how to run:
>    QEMU=/foo/qemu-system-x86_64 x86/run x86/hpet_read_test.flat -smp X
> where X is desired (max) number of logical CPUs on host
> 
> it will 1st execute concurrent read benchmark
> and after that it will run torture test enabling/disabling HPET counter,
> while running readers in parallel. Goal is to verify counter that always
> goes up.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> v2:
>    * fix broken timer going backwards check
>    * report # of fails
>    * warn if number of vcpus is not sufficient for torture test and skip
>      it
>    * style fixups
> ---
>  x86/Makefile.common  |  2 ++
>  x86/hpet_read_test.c | 73 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 75 insertions(+)
>  create mode 100644 x86/hpet_read_test.c
> 
> diff --git a/x86/Makefile.common b/x86/Makefile.common
> index 5663a65d..ef0e09a6 100644
> --- a/x86/Makefile.common
> +++ b/x86/Makefile.common
> @@ -101,6 +101,8 @@ tests-common += $(TEST_DIR)/realmode.$(exe) \
>  realmode_bits := $(if $(call cc-option,-m16,""),16,32)
>  endif
>  
> +tests-common += $(TEST_DIR)/hpet_read_test.$(exe)
> +
>  test_cases: $(tests-common) $(tests)
>  
>  $(TEST_DIR)/%.o: CFLAGS += -std=gnu99 -ffreestanding -I $(SRCDIR)/lib -I $(SRCDIR)/lib/x86 -I lib
> diff --git a/x86/hpet_read_test.c b/x86/hpet_read_test.c
> new file mode 100644
> index 00000000..a14194e6
> --- /dev/null
> +++ b/x86/hpet_read_test.c
> @@ -0,0 +1,73 @@
> +#include "libcflat.h"
> +#include "smp.h"
> +#include "asm/barrier.h"
> +#include "x86/atomic.h"
> +
> +#define HPET_ADDR         0xFED00000L
> +#define HPET_COUNTER_ADDR ((uint8_t *)HPET_ADDR + 0xF0UL)
> +#define HPET_CONFIG_ADDR  ((uint8_t *)HPET_ADDR + 0x10UL)
> +#define HPET_ENABLE_BIT   0x01UL
> +#define HPET_CLK_PERIOD   10
> +
> +static atomic_t fail;
> +
> +static void hpet_reader(void *data)
> +{
> +	uint64_t old_counter = 0, new_counter;
> +	long cycles = (long)data;
> +
> +	while (cycles--) {
> +		new_counter = *(volatile uint64_t *)HPET_COUNTER_ADDR;
> +		if (new_counter < old_counter) {
> +			atomic_inc(&fail);
> +		}
> +		old_counter = new_counter;
> +	}
> +}
> +
> +static void hpet_writer(void *data)
> +{
> +	int i;
> +	long cycles = (long)data;
> +
> +	for (i = 0; i < cycles; ++i)
> +		if (i % 2)
> +			*(volatile uint64_t *)HPET_CONFIG_ADDR |= HPET_ENABLE_BIT;
> +		else
> +			*(volatile uint64_t *)HPET_CONFIG_ADDR &= ~HPET_ENABLE_BIT;
> +}
> +
> +int main(void)
> +{
> +	long cycles = 100000;
> +	int i;
> +	int ncpus;
> +	uint64_t start, end, time_ns;
> +
> +	ncpus = cpu_count();
> +	do {
> +		printf("* starting concurrent read bench on %d cpus\n", ncpus);
> +		*(volatile uint64_t *)HPET_CONFIG_ADDR |= HPET_ENABLE_BIT;
> +		start = *(volatile uint64_t *)HPET_COUNTER_ADDR;
> +		on_cpus(hpet_reader, (void *)cycles);
> +		end = (*(volatile uint64_t *)HPET_COUNTER_ADDR);
> +		time_ns = (end - start) * HPET_CLK_PERIOD;
> +		report(time_ns && !atomic_read(&fail),
> +			"read test took %lu ms, avg read: %lu ns\n", time_ns/1000000,  time_ns/cycles);
> +	} while (0);
> +
> +	do {
> +		printf("* starting enable/disable with concurent readers torture\n");
> +		if (ncpus > 2) {
> +			for (i = 2; i < ncpus; i++)
> +			    on_cpu_async(i, hpet_reader, (void *)cycles);
> +
> +			on_cpu(1, hpet_writer, (void *)cycles);
> +			report(!atomic_read(&fail), "torture test, fails: %u\n", atomic_read(&fail));
> +		} else {
> +			printf("SKIP: torture test: '-smp X' should be greater than 2\n");
> +	}
> +	} while (0);
> +
> +	return report_summary();
> +}