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From: Daniel Vetter <daniel@ffwll.ch>
To: Ben Widawsky <ben@bwidawsk.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 2/3] drm/i915: close PM interrupt masking races in the rps work func
Date: Sun, 4 Sep 2011 21:26:48 +0200
Message-ID: <20110904192648.GB2799@phenom.ffwll.local> (raw)
In-Reply-To: <20110904100817.16c6c4cc@bwidawsk.net>

On Sun, Sep 04, 2011 at 10:08:17AM -0700, Ben Widawsky wrote:
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 55518e3..3bc1479 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -415,12 +415,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
>         gen6_set_rps(dev_priv->dev, new_delay);
>         dev_priv->cur_delay = new_delay;
>  
> -       /*
> -        * rps_lock not held here because clearing is non-destructive. There is
> -        * an *extremely* unlikely race with gen6_rps_enable() that is prevented
> -        * by holding struct_mutex for the duration of the write.
> -        */
> -       I915_WRITE(GEN6_PMIMR, pm_imr & ~pm_iir);
> +       I915_WRITE(GEN6_PMIMR, pm_imr & dev_priv->pm_iir);
>         mutex_unlock(&dev_priv->dev->struct_mutex);
>  }

For this to work we'd need to hold the rps_lock (to avoid racing with the
irq handler). But imo my approach is conceptually simpler: The work func
grabs all oustanding PM interrupts and then enables them again in one go
(protected by rps_lock). And because the dev_priv->wq workqueue is
single-threaded (no point in using multiple threads when all work items
grab dev->struct mutex) we also cannot make a mess by running work items
in the wrong order (or in parallel).

-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48

  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-09-04  3:24 [PATCH] drm/i915: Fix rps irq warning Ben Widawsky
2011-09-04  9:03 ` Chris Wilson
2011-09-04 15:49   ` Ben Widawsky
2011-09-04 15:34     ` [PATCH 0/3] slaughter rps races some more Daniel Vetter
2011-09-04 15:35       ` [PATCH 1/3] drm/i915: close PM interrupt masking races in the irq handler Daniel Vetter
2011-09-04 17:09         ` Ben Widawsky
2011-09-04 15:35       ` [PATCH 2/3] drm/i915: close PM interrupt masking races in the rps work func Daniel Vetter
2011-09-04 17:08         ` Ben Widawsky
2011-09-04 19:26           ` Daniel Vetter [this message]
2011-09-04 19:56             ` Ben Widawsky
2011-09-04 20:10               ` Daniel Vetter
2011-09-04 21:38                 ` Ben Widawsky
2011-09-05  6:38                   ` Daniel Vetter
2011-09-05  6:51                     ` Ben Widawsky
2011-09-05 12:15                       ` Chris Wilson
2011-09-04 15:35       ` [PATCH 3/3] drm/i915: close rps work vs. rps disable races Daniel Vetter
2011-09-04 17:23         ` Ben Widawsky
2011-09-04 19:17           ` Daniel Vetter
2011-09-04 19:50             ` Ben Widawsky
2011-09-04 19:57               ` Daniel Vetter
2011-09-05  8:15                 ` [PATCH] drm/i915: properly cancel rps_work on module unload Daniel Vetter
2011-09-05 17:27                   ` Ben Widawsky
2011-09-08 12:00 [PATCH 1/3] drm/i915: close PM interrupt masking races in the irq handler Daniel Vetter
2011-09-08 12:00 ` [PATCH 2/3] drm/i915: close PM interrupt masking races in the rps work func Daniel Vetter
2011-09-08 15:19   ` Ben Widawsky

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