On Thu, Mar 28, 2013 at 01:00:56PM +0200, Ville Syrjälä wrote:
> On Thu, Mar 28, 2013 at 12:03:25AM +0100, Daniel Vetter wrote:
> > As Thomas Gleixner spotted, it's rather horrible racy:
> > - We can miss almost a full tick, so need to compensate by 1 jiffy.
>
> I have a feeling this is a rather common pattern, so I wonder
> if [mu]secs_to_jiffies() should do the +1 already for everyone.
> Or maybe there should be some other macros for specifying
> timeouts that would do the +1.
>
> > - We need to re-check the condition when having timed-out, since a
> > the last check could have been before the timeout expired. E.g. when
> > we've been preempted or a long irq happened.
> >
> > Cc: Thomas Gleixner <[email protected]>
> > Reported-by: Jack Winter <[email protected]>
> > Cc: Jack Winter <[email protected]>
> > Signed-off-by: Daniel Vetter <[email protected]>
>
> Reviewed-by: Ville Syrjälä <[email protected]>
Merged both patches, thanks for the review.
-Daniel
>
> > ---
> > drivers/gpu/drm/i915/intel_drv.h | 13 +++++++++++--
> > 1 file changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h
> > b/drivers/gpu/drm/i915/intel_drv.h
> > index c8c1979..9dcae4e 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -33,12 +33,21 @@
> > #include <drm/drm_fb_helper.h>
> > #include <drm/drm_dp_helper.h>
> >
> > +/**
> > + * _wait_for - magic (register) wait macro
> > + *
> > + * Does the right thing for modeset paths when run under kdgb or similar
> > atomic
> > + * contexts. Note that it's important that we check the condition again
> > after
> > + * having timed out, since the timeout could be due to preemption or
> > similar and
> > + * we've never had a chance to check the condition before the timeout.
> > + */
> > #define _wait_for(COND, MS, W) ({ \
> > - unsigned long timeout__ = jiffies + msecs_to_jiffies(MS); \
> > + unsigned long timeout__ = jiffies + msecs_to_jiffies(MS) + 1; \
> > int ret__ = 0; \
> > while (!(COND)) { \
> > if (time_after(jiffies, timeout__)) { \
> > - ret__ = -ETIMEDOUT; \
> > + if (!(COND)) \
> > + ret__ = -ETIMEDOUT; \
> > break; \
> > } \
> > if (W && drm_can_sleep()) { \
> > --
> > 1.7.11.7
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > [email protected]
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> --
> Ville Syrjälä
> Intel OTC
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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