[Intel-gfx] [CI 1/2] drm/i915: Use ktime on wait_for

[Lucas De Marchi]

On Mon, Apr 23, 2018 at 4:37 AM, Mika Kuoppala
<mika.kuoppala at linux.intel.com> wrote:
> We use jiffies to determine when wait expires. However
> Imre did find out that jiffies can and will do a >1
> increments on certain situations [1]. When this happens
> in a wait_for loop, we return timeout errorneously
> much earlier than what the real wallclock would say.
>
> We can't afford our waits to timeout prematurely.

Isn't this also the reason why we have *_to_jiffies_timeout() family
of functions? Should those
be converted as well?

Lucas De Marchi

> Discard jiffies and change to ktime to detect timeouts.
>
> v2: added bugzilla entry (Imre), added stable (Chris)
>
> Reported-by: Imre Deak <imre.deak at intel.com>
> References: https://lkml.org/lkml/2018/4/18/798 [1]
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105771
> Cc: Imre Deak <imre.deak at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_drv.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 44ed248f1fe9..33ff2638c92b 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -49,12 +49,12 @@
>   * check the condition before the timeout.
>   */
>  #define __wait_for(OP, COND, US, Wmin, Wmax) ({ \
> -       unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1;   \
> +       const ktime_t end__ = ktime_add_ns(ktime_get_raw(), 1000ll * (US)); \
>         long wait__ = (Wmin); /* recommended min for usleep is 10 us */ \
>         int ret__;                                                      \
>         might_sleep();                                                  \
>         for (;;) {                                                      \
> -               bool expired__ = time_after(jiffies, timeout__);        \
> +               const bool expired__ = ktime_after(ktime_get_raw(), end__); \
>                 OP;                                                     \
>                 if (COND) {                                             \
>                         ret__ = 0;                                      \
> --
> 2.14.1
>
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-- 
Lucas De Marchi