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* [PATCH v2] x86: add HPET counter read micro benchmark and enable/disable torture tests
@ 2025-07-14 14:50 Igor Mammedov
  2025-07-18 15:58 ` Igor Mammedov
  0 siblings, 1 reply; 2+ messages in thread
From: Igor Mammedov @ 2025-07-14 14:50 UTC (permalink / raw)
  To: kvm; +Cc: pbonzini

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

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();
+}
-- 
2.47.1


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