[Intel-gfx] [PATCH 01/26] drm/i915/ringbuffer: Reload PDs harder on byt/bcs

[Joonas Lahtinen]

Quoting Chris Wilson (2018-09-11 14:57:45)
> Baytrail takes a little more convincing that it needs to actually reload
> its Page Directoy (ppGTT) before the context switch, so repeat it until
> it gets the message. Once again the arbitrary values here are
> empirically derived.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107861
> Testcase: igt/gem_exec_parallel/fds
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 472939f5c18f..d0ef50bf930a 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1677,9 +1677,26 @@ static int switch_context(struct i915_request *rq)
>         GEM_BUG_ON(HAS_EXECLISTS(rq->i915));
>  
>         if (ppgtt) {
> -               ret = load_pd_dir(rq, ppgtt);
> -               if (ret)
> -                       goto err;
> +               int loops;
> +
> +               /*
> +                * Baytail takes a little more convincing that it really needs
> +                * to reload the PD between contexts. It is not just a little
> +                * longer, as adding more stalls after the load_pd_dir (i.e.
> +                * adding a long loop around flush_pd_dir) is not as effective
> +                * as reloading the PD umpteen times. 32 is derived from
> +                * experimentation (gem_exec_parallel/fds) and has no good
> +                * explanation.
> +                */
> +               loops = 1;
> +               if (engine->id == BCS && IS_VALLEYVIEW(engine->i915))
> +                       loops = 32;
> +
> +               do {
> +                       ret = load_pd_dir(rq, ppgtt);
> +                       if (ret)
> +                               goto err;
> +               } while (--loops);

This what they call black magic.

Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>

Regards, Joonas