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

[Tvrtko Ursulin]

On 16/11/15 12:55, Chris Wilson wrote:
> On Mon, Nov 16, 2015 at 12:08:08PM +0000, Tvrtko Ursulin wrote:
> > On 16/11/15 11:12, Chris Wilson wrote:
> > > On Mon, Nov 16, 2015 at 10:24:45AM +0000, Tvrtko Ursulin wrote:
> > > > On 15/11/15 13:32, Chris Wilson wrote:
> > > > > +static u64 local_clock_us(unsigned *cpu)
> > > > > +{
> > > > > +	u64 t;
> > > > > +
> > > > > +	*cpu = get_cpu();
> > > > > +	t = local_clock() >> 10;
> > > >
> > > > Needs comment I think to explicitly mention the approximation, or
> > > > maybe drop the _us suffix?
> > >
> > > I did consider _approx_us but thought that was overkill. A comment along
> > > the lines of
> > > /* Approximately convert ns to us - the error is less than the
> > >   * truncation!
> > >   */
> >
> > And the result is not used in subsequent calculations apart from
> > comparing against an approximate timeout?
>
> Exactly, the timeout is fairly arbitrary and defined in the same units.
> That we truncate is a much bigger cause for concern in terms of spinning
> accurately for a definite length of time.

Bah sorry that was not supposed to be a question but a suggestion to add 
to the comment. Must had mistyped the question mark. :)

Regards,

Tvrtko
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