Re: __i915_spin_request() sucks

From	Mike Galbraith <umgwanakikbuti@gmail.com>
Newsgroups	linux.kernel
Subject	Re: __i915_spin_request() sucks
Date	2015-11-13 17:20 +0100
Message-ID	<qupeX-eJ-27@gated-at.bofh.it> (permalink)
References	(1 earlier) <qu6YF-5kL-3@gated-at.bofh.it> <qu8nM-6oo-35@gated-at.bofh.it> <qu90u-6Bs-13@gated-at.bofh.it> <quiGu-4vC-19@gated-at.bofh.it> <quoCf-8cf-47@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, 2015-11-13 at 08:36 -0700, Jens Axboe wrote:
> Previous patch was obvious pre-coffee crap, this should work for using
> ktime to spin max 1usec.

1us seems a tad low.  I doubt the little wooden gears and pulleys of my
core2 Toshiba Satellite lappy can get one loop ground out in a usec :)

> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 5cf4a1998273..21192e55c33c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1148,17 +1148,18 @@ static bool missed_irq(struct drm_i915_private *dev_priv,
>  
>  static int __i915_spin_request(struct drm_i915_gem_request *req)
>  {
> -	unsigned long timeout;
> +	ktime_t timeout;
>  
>  	if (i915_gem_request_get_ring(req)->irq_refcount)
>  		return -EBUSY;
>  
> -	timeout = jiffies + 1;
> +	timeout = ktime_get();
> +	ktime_add_us(timeout, 1);
>  	while (!need_resched()) {
>  		if (i915_gem_request_completed(req, true))
>  			return 0;
>  
> -		if (time_after_eq(jiffies, timeout))
> +		if (ktime_after(ktime_get(), timeout))
>  			break;
>  
>  		cpu_relax_lowlatency();
> 


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Thread

__i915_spin_request() sucks Jens Axboe <axboe@kernel.dk> - 2015-11-12 21:40 +0100
  Re: __i915_spin_request() sucks Jens Axboe <axboe@kernel.dk> - 2015-11-12 21:50 +0100
    Re: __i915_spin_request() sucks Chris Wilson <chris@chris-wilson.co.uk> - 2015-11-12 23:20 +0100
      Re: __i915_spin_request() sucks Jens Axboe <axboe@kernel.dk> - 2015-11-13 00:00 +0100
        Re: __i915_spin_request() sucks Jens Axboe <axboe@kernel.dk> - 2015-11-13 00:00 +0100
        Re: __i915_spin_request() sucks Chris Wilson <chris@chris-wilson.co.uk> - 2015-11-13 10:20 +0100
          Re: __i915_spin_request() sucks Jens Axboe <axboe@kernel.dk> - 2015-11-13 16:20 +0100
          Re: __i915_spin_request() sucks Jens Axboe <axboe@kernel.dk> - 2015-11-13 16:40 +0100
            Re: __i915_spin_request() sucks Mike Galbraith <umgwanakikbuti@gmail.com> - 2015-11-13 17:20 +0100
              Re: __i915_spin_request() sucks Jens Axboe <axboe@kernel.dk> - 2015-11-13 17:30 +0100
                Re: __i915_spin_request() sucks Chris Wilson <chris@chris-wilson.co.uk> - 2015-11-13 23:20 +0100
                Re: __i915_spin_request() sucks Jens Axboe <axboe@kernel.dk> - 2015-11-13 23:20 +0100

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