[PATCH igt] igt/perf_pmu: Avoid underflow in measured_sleep()

[PATCH igt] igt/perf_pmu: Avoid underflow in measured_sleep()

[Chris Wilson]

Be careful not to underflow into a very large positive usec value and so
sleep forever^W until boredom kicks in.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
 tests/perf_pmu.c | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
index 5d5f2b30..e153aaf3 100644
--- a/tests/perf_pmu.c
+++ b/tests/perf_pmu.c
@@ -111,22 +111,17 @@ static void pmu_read_multi(int fd, unsigned int num, uint64_t *val)
  */
 static unsigned int measured_usleep(unsigned int usec)
 {
-	uint64_t slept = 0;
-
-	while (usec > 0) {
-		struct timespec start = { };
-		uint64_t this_sleep;
+	struct timespec ts = { };
+	unsigned int slept;
 
-		igt_nsec_elapsed(&start);
-		usleep(usec);
-		this_sleep = igt_nsec_elapsed(&start);
-		slept += this_sleep;
-		if (this_sleep > usec * 1000)
-			break;
-		usec -= this_sleep;
-	}
+	slept = igt_nsec_elapsed(&ts);
+	igt_assert(slept == 0);
+	do {
+		usleep(usec - slept);
+		slept = igt_nsec_elapsed(&ts) / 1000;
+	} while (slept < usec);
 
-	return slept;
+	return igt_nsec_elapsed(&ts);
 }
 
 static unsigned int e2ring(int gem_fd, const struct intel_execution_engine2 *e)
-- 
2.15.0

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Re: [PATCH igt] igt/perf_pmu: Avoid underflow in measured_sleep()

[Tvrtko Ursulin]

On 22/11/2017 20:14, Chris Wilson wrote:
> Be careful not to underflow into a very large positive usec value and so
> sleep forever^W until boredom kicks in.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   tests/perf_pmu.c | 23 +++++++++--------------
>   1 file changed, 9 insertions(+), 14 deletions(-)
> 
> diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
> index 5d5f2b30..e153aaf3 100644
> --- a/tests/perf_pmu.c
> +++ b/tests/perf_pmu.c
> @@ -111,22 +111,17 @@ static void pmu_read_multi(int fd, unsigned int num, uint64_t *val)
>    */
>   static unsigned int measured_usleep(unsigned int usec)
>   {
> -	uint64_t slept = 0;
> -
> -	while (usec > 0) {
> -		struct timespec start = { };
> -		uint64_t this_sleep;
> +	struct timespec ts = { };
> +	unsigned int slept;
>   
> -		igt_nsec_elapsed(&start);
> -		usleep(usec);
> -		this_sleep = igt_nsec_elapsed(&start);
> -		slept += this_sleep;
> -		if (this_sleep > usec * 1000)
> -			break;
> -		usec -= this_sleep;
> -	}
> +	slept = igt_nsec_elapsed(&ts);
> +	igt_assert(slept == 0);
> +	do {
> +		usleep(usec - slept);
> +		slept = igt_nsec_elapsed(&ts) / 1000;
> +	} while (slept < usec);
>   
> -	return slept;
> +	return igt_nsec_elapsed(&ts);
>   }
>   
>   static unsigned int e2ring(int gem_fd, const struct intel_execution_engine2 *e)
> 

Looks OK. Silly bug of mine and I wonder how I was so lucky not to hit 
it all this time.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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✗ Fi.CI.BAT: failure for igt/perf_pmu: Avoid underflow in measured_sleep()

[Patchwork]

== Series Details ==

Series: igt/perf_pmu: Avoid underflow in measured_sleep()
URL   : https://patchwork.freedesktop.org/series/34252/
State : failure

== Summary ==

Series 34252 revision 1 was fully merged or fully failed: no git log

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