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 number of logical CPUs to test with

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>
---
v4:
   * use global for test cycles and siplify code a bit
   * use cpu number instead of APCI ID as index into latency array
   * report failure if a cpu measured 0 latency
   * replace on_cpus() with on_cpu_async() to avoid BSP
     interrupting itself
   * drop volatile

v3:
   * measure lat inside threads so that, threads startup time wouldn't
     throw off results
   * fix BSP iterrupting itself by running read test and stalling
     other cpus as result. (fix it by exiting read test earlier if
     it's running on BSP)
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 | 93 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 95 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..a44cdac2
--- /dev/null
+++ b/x86/hpet_read_test.c
@@ -0,0 +1,93 @@
+#include "libcflat.h"
+#include "smp.h"
+#include "apic.h"
+#include "asm/barrier.h"
+#include "x86/atomic.h"
+#include "vmalloc.h"
+#include "alloc.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
+
+#define TEST_CYCLES 100000
+
+static atomic_t fail;
+static uint64_t latency[MAX_TEST_CPUS];
+
+static void hpet_reader(void *data)
+{
+	long i;
+	uint64_t old_counter = 0, new_counter;
+	long id = (long)data;
+
+	latency[id] = *(uint64_t *)HPET_COUNTER_ADDR;
+	for (i = 0; i < TEST_CYCLES; ++i) {
+		new_counter = *(uint64_t *)HPET_COUNTER_ADDR;
+		if (new_counter < old_counter)
+			atomic_inc(&fail);
+		old_counter = new_counter;
+	}
+	/* claculate job latency in ns */
+	latency[id] = (*(uint64_t *)HPET_COUNTER_ADDR - latency[id])
+		* HPET_CLK_PERIOD / TEST_CYCLES;
+}
+
+static void hpet_writer(void *data)
+{
+	int i;
+
+	for (i = 0; i < TEST_CYCLES; ++i)
+		if (i % 2)
+			*(uint64_t *)HPET_CONFIG_ADDR |= HPET_ENABLE_BIT;
+		else
+			*(uint64_t *)HPET_CONFIG_ADDR &= ~HPET_ENABLE_BIT;
+}
+
+int main(void)
+{
+	unsigned long cpu, time_ns, lat = 0;
+	uint64_t start, end;
+	int ncpus = cpu_count();
+
+	do {
+		printf("* starting concurrent read bench on %d cpus\n", ncpus);
+		*(uint64_t *)HPET_CONFIG_ADDR |= HPET_ENABLE_BIT;
+		start = *(uint64_t *)HPET_COUNTER_ADDR;
+
+		for (cpu = cpu_count() - 1; cpu > 0; --cpu)
+			on_cpu_async(cpu, hpet_reader, (void *)cpu);
+		while (cpus_active() > 1)
+			pause();
+
+		end = (*(uint64_t *)HPET_COUNTER_ADDR);
+		time_ns = (end - start) * HPET_CLK_PERIOD;
+
+		for (cpu = 1; cpu < ncpus; cpu++)
+			if (latency[cpu])
+				lat += latency[cpu];
+			else
+				report_fail("cpu %lu reported invalid latency (0)\n", cpu);
+		lat = lat / ncpus;
+
+		report(time_ns && !atomic_read(&fail),
+			"read test took %lu ms, avg read: %lu ns\n", time_ns/1000000,  lat);
+	} while (0);
+
+	do {
+		printf("* starting enable/disable with concurrent readers torture\n");
+		if (ncpus > 2) {
+			for (cpu = 2; cpu < ncpus; cpu++)
+				on_cpu_async(cpu, hpet_reader, (void *)TEST_CYCLES);
+
+			on_cpu(1, hpet_writer, (void *)TEST_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