From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
Thomas Gleixner <tglx@linutronix.de>,
Jack Winter <jbh@alchemy.lu>
Subject: Re: [PATCH 2/2] drm/i915: fix up _wait_for macro
Date: Thu, 28 Mar 2013 13:00:56 +0200 [thread overview]
Message-ID: <20130328110056.GK4469@intel.com> (raw)
In-Reply-To: <1364425405-1200-2-git-send-email-daniel.vetter@ffwll.ch>
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
--
Ville Syrjälä
Intel OTC
next prev parent reply other threads:[~2013-03-28 11:01 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-27 23:03 [PATCH 1/2] drm/i915: fold wait_for_atomic_us into wait_for_atomic Daniel Vetter
2013-03-27 23:03 ` [PATCH 2/2] drm/i915: fix up _wait_for macro Daniel Vetter
2013-03-28 11:00 ` Ville Syrjälä [this message]
2013-03-28 15:41 ` Daniel Vetter
2013-03-28 10:32 ` [PATCH 1/2] drm/i915: fold wait_for_atomic_us into wait_for_atomic Ville Syrjälä
2013-03-28 10:31 ` [PATCH] " Daniel Vetter
2013-03-28 10:53 ` Ville Syrjälä
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