[Intel-gfx] [PATCH 1/6] drm/i915/gem: Almagamate clflushes on suspend

[Matthew Auld]

On Tue, 19 Jan 2021 at 14:49, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>
> When flushing objects larger than the CPU cache it is preferrable to use
> a single wbinvd() rather than overlapping clflush(). At runtime, we
> avoid wbinvd() due to its system-wide latencies, but during
> singlethreaded suspend, no one will observe the imposed latency and we
> can opt for the faster wbinvd to clear all objects in a single hit.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_pm.c | 40 +++++++++-----------------
>  1 file changed, 13 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pm.c b/drivers/gpu/drm/i915/gem/i915_gem_pm.c
> index 40d3e40500fa..38c1298cb14b 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_pm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pm.c
> @@ -11,6 +11,12 @@
>
>  #include "i915_drv.h"
>
> +#if defined(CONFIG_X86)
> +#include <asm/smp.h>
> +#else
> +#define wbinvd_on_all_cpus()
> +#endif
> +
>  void i915_gem_suspend(struct drm_i915_private *i915)
>  {
>         GEM_TRACE("%s\n", dev_name(i915->drm.dev));
> @@ -32,13 +38,6 @@ void i915_gem_suspend(struct drm_i915_private *i915)
>         i915_gem_drain_freed_objects(i915);
>  }
>
> -static struct drm_i915_gem_object *first_mm_object(struct list_head *list)
> -{
> -       return list_first_entry_or_null(list,
> -                                       struct drm_i915_gem_object,
> -                                       mm.link);
> -}
> -
>  void i915_gem_suspend_late(struct drm_i915_private *i915)
>  {
>         struct drm_i915_gem_object *obj;
> @@ -48,6 +47,7 @@ void i915_gem_suspend_late(struct drm_i915_private *i915)
>                 NULL
>         }, **phase;
>         unsigned long flags;
> +       bool flush = false;
>
>         /*
>          * Neither the BIOS, ourselves or any other kernel
> @@ -73,29 +73,15 @@ void i915_gem_suspend_late(struct drm_i915_private *i915)
>
>         spin_lock_irqsave(&i915->mm.obj_lock, flags);
>         for (phase = phases; *phase; phase++) {
> -               LIST_HEAD(keep);
> -
> -               while ((obj = first_mm_object(*phase))) {
> -                       list_move_tail(&obj->mm.link, &keep);
> -
> -                       /* Beware the background _i915_gem_free_objects */
> -                       if (!kref_get_unless_zero(&obj->base.refcount))
> -                               continue;
> -
> -                       spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
> -
> -                       i915_gem_object_lock(obj, NULL);
> -                       drm_WARN_ON(&i915->drm,
> -                           i915_gem_object_set_to_gtt_domain(obj, false));
> -                       i915_gem_object_unlock(obj);
> -                       i915_gem_object_put(obj);
> -
> -                       spin_lock_irqsave(&i915->mm.obj_lock, flags);
> +               list_for_each_entry(obj, *phase, mm.link) {
> +                       if (!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_READ))
> +                               flush |= (obj->read_domains & I915_GEM_DOMAIN_CPU) == 0;
> +                       __start_cpu_write(obj); /* presume auto-hibernate */
>                 }
> -
> -               list_splice_tail(&keep, *phase);
>         }
>         spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
> +       if (flush)
> +               wbinvd_on_all_cpus();

Hmmm, this builds on !CONFIG_X86?

>  }
>
>  void i915_gem_resume(struct drm_i915_private *i915)
> --
> 2.20.1
>
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