| Message ID | 1364425405-1200-2-git-send-email-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <tglx@linutronix.de> > Reported-by: Jack Winter <jbh@alchemy.lu> > Cc: Jack Winter <jbh@alchemy.lu> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> > --- > 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 > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
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 <tglx@linutronix.de> > > Reported-by: Jack Winter <jbh@alchemy.lu> > > Cc: Jack Winter <jbh@alchemy.lu> > > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> > > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> 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 > > Intel-gfx@lists.freedesktop.org > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx > > -- > Ville Syrjälä > Intel OTC
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()) { \
As Thomas Gleixner spotted, it's rather horrible racy: - We can miss almost a full tick, so need to compensate by 1 jiffy. - 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 <tglx@linutronix.de> Reported-by: Jack Winter <jbh@alchemy.lu> Cc: Jack Winter <jbh@alchemy.lu> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> --- drivers/gpu/drm/i915/intel_drv.h | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)