> > > Ok. But W is still just a random value we picked for being the
> > > mininum legal value for msleep(). So just usleep_range(500, 2000)
> > > or somesuch will be fine. We can rename W to CAN_SLEEP it that helps.
> >
> > We do use _wait_for directly from intel_dp.c with W == 10 to not retry so many times on what's expected to be a long wait.
>
> Hmm, missed that. We can fallback to the fallback plan of switching
> based on W between msleep and usleep_range. Using -1, would be best.
>
> if (W && drm_can_sleep()) {
> if (__builtin_constant_p(W) && W < 0)
> usleep_range(500, 2000);
> else
> msleep(W);
> }
>
Seems to be a good approach, will take care of this in the next version of the patch.
> > Its not expected to be too long, we tend to get vblank every 16ms.
> > With using usleep_range with min and max as 1-2ms, we have observed that this function consuming 4ms to 17ms.
>
> vs msleep()? That would be nice information to capture in the changelog.
> We expect the average wait here to be 8ms, ofc.
>
Sure, will add this in the changelog.
> > Having 10ms sleep timer, we might tend to be blocking for 6ms in
> > some cases.(from the above data) Moreover 10ms usleep doesn't
> > guarantee that we get a chance to execute after 10ms, it might get increased due to scheduling. So ideal solution would be to use useep_range which uses hrtimers.
>
> Ideal for what? We only use the sleeping path where we do not care too
> great about the latency, otherwise we use the busy-wait path.
> Improving the latency of the sleep without adversely affecting overall
> system performance/power is ideal.
We've used it in a few places where we'd care a bit more about latency (like edid reads) but on most platforms those switched to interrupts now.
-Daniel
Thanks and Regards,
Arun R Murthy
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