linux-kernel - Re: [PATCH 2/2] drm/i915: Limit the busy wait on requests to 2us not 10ms!

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Date:	Thu, 3 Dec 2015 23:03:17 +0100
From:	Pavel Machek <pavel@....cz>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Jens Axboe <axboe@...nel.dk>, intel-gfx@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
	Eero Tamminen <eero.t.tamminen@...el.com>,
	"Rantala, Valtteri" <valtteri.rantala@...el.com>,
	stable@...nel.vger.org
Subject: Re: [PATCH 2/2] drm/i915: Limit the busy wait on requests to 2us not
 10ms!

Hi!

> Reported-by: Jens Axboe <axboe@...nel.dk>
> Link: https://lkml.org/lkml/2015/11/12/621
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc; "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@...el.com>
> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
> Cc: Eero Tamminen <eero.t.tamminen@...el.com>
> Cc: "Rantala, Valtteri" <valtteri.rantala@...el.com>
> Cc: stable@...nel.vger.org
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 28 +++++++++++++++++++++++++---
>  1 file changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 740530c571d1..2a88158bd1f7 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1146,14 +1146,36 @@ static bool missed_irq(struct drm_i915_private *dev_priv,
>  	return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
>  }
>  
> +static u64 local_clock_us(unsigned *cpu)
> +{
> +	u64 t;
> +
> +	*cpu = get_cpu();
> +	t = local_clock() >> 10;
> +	put_cpu();
> +
> +	return t;
> +}
> +
> +static bool busywait_stop(u64 timeout, unsigned cpu)
> +{
> +	unsigned this_cpu;
> +
> +	if (time_after64(local_clock_us(&this_cpu), timeout))
> +		return true;
> +
> +	return this_cpu != cpu;
> +}

Perhaps you want to ask the timekeeping people for the right
primitive? I guess you are not the only one needing this..
									Pavel
									
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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