[igt-dev] [PATCH i-g-t] tests/perf_pmu: Avoid off-lining all CPUs

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-02-19 13:40:37)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Bail out from the cpu-hotplug test if we failed to bring a CPU back
> online.
> 
> This still leaves the machine in a quite bad state, but at least it
> avoids hard hanging it.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  tests/perf_pmu.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/tests/perf_pmu.c b/tests/perf_pmu.c
> index 7fab73e22c2d..a334d3b5770e 100644
> --- a/tests/perf_pmu.c
> +++ b/tests/perf_pmu.c
> @@ -965,6 +965,7 @@ static void cpu_hotplug(int gem_fd)
>         int link[2];
>         int fd, ret;
>         int cur = 0;
> +       char buf;
>  
>         igt_require(cpu0_hotplug_support());
>  
> @@ -1012,7 +1013,15 @@ static void cpu_hotplug(int gem_fd)
>                         /* Offline followed by online a CPU. */
>                         igt_assert_eq(write(cpufd, "0", 2), 2);
>                         usleep(1e6);
> -                       igt_assert_eq(write(cpufd, "1", 2), 2);
> +                       ret = write(cpufd, "1", 2);
> +                       if (ret < 0) {
> +                               /*
> +                                * Abort the test if we failed to bring a CPU
> +                                * back online.
> +                                */
> +                               igt_assert_eq(write(link[1], "s", 1), 1);
> +                               break;
> +                       }
>  
>                         close(cpufd);
>                         cpu++;
> @@ -1026,7 +1035,6 @@ static void cpu_hotplug(int gem_fd)
>          * until the CPU core shuffler finishes one loop.
>          */
>         for (;;) {
> -               char buf;
>                 int ret2;
>  
>                 usleep(500e3);
> @@ -1053,6 +1061,9 @@ static void cpu_hotplug(int gem_fd)
>         close(fd);
>         close(link[0]);
>  
> +       /* Skip if child signals a problem with bringing a CPU back online. */
> +       igt_skip_on(buf == 's');

The logic makes sense.
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

What happens if we try to online an already on cpu? Will that report the
failure or just tell us to stop wasting its time?
-Chris