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benchmarks/gem_latency: Serialise mmio reads

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The joy of our hardware; don't let two threads attempt to read the same
register at the same time.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
This commit is contained in:
Chris Wilson 2015-12-21 12:53:21 +00:00
parent 3ebce37b65
commit a1d465a3c5
1 changed files with 28 additions and 4 deletions
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32
benchmarks/gem_latency.c
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@ -46,10 +46,29 @@
static int done;
static int fd;
static volatile uint32_t *timestamp_reg;
static pthread_spinlock_t timestamp_lock;
#define REG(x) (volatile uint32_t *)((volatile char *)igt_global_mmio + x)
#define REG_OFFSET(x) ((volatile char *)(x) - (volatile char *)igt_global_mmio)
static uint32_t read_timestamp_unlocked(void)
{
return *timestamp_reg;
}
static uint32_t read_timestamp_locked(void)
{
uint32_t t;
pthread_spin_lock(&timestamp_lock);
t = *timestamp_reg;
pthread_spin_unlock(&timestamp_lock);
return t;
}
static uint32_t (*read_timestamp)(void) = read_timestamp_unlocked;
struct consumer {
pthread_t thread;
@ -247,7 +266,7 @@ static void setup_nop(struct producer *p, uint32_t batch)
static void measure_latency(struct producer *p, igt_stats_t *stats)
{
gem_sync(fd, p->latency_dispatch.exec[0].handle);
igt_stats_push(stats, *timestamp_reg - *p->last_timestamp);
igt_stats_push(stats, read_timestamp() - *p->last_timestamp);
}
static void *producer(void *arg)
@ -256,7 +275,7 @@ static void *producer(void *arg)
int n;
while (!done) {
uint32_t start = *timestamp_reg;
uint32_t start = read_timestamp();
int batches;
/* Control the amount of work we do, similar to submitting
@ -391,9 +410,14 @@ static int run(int seconds,
else
timestamp_reg = REG(BCS_TIMESTAMP);
nrun = *timestamp_reg;
if (gen < 8) {
pthread_spin_init(&timestamp_lock, 0);
read_timestamp = read_timestamp_locked;
}
nrun = read_timestamp();
usleep(1);
if (*timestamp_reg == nrun)
if (read_timestamp() == nrun)
return 77;
scratch = gem_create(fd, 4*WIDTH*HEIGHT);