Re: [PATCH 2/5] drm/i915: Remove redundant TLB invalidate on switching ppgtt

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> We are required to reload the TLBs around ppgtt switches. However, we
> already do an unconditional TLB invalidate before every batch and a flush
> afterwards, so this condition is already satisfied without extra flushes
> around the LRI instructions.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c | 17 -----------------
>  1 file changed, 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 057239ab3f70..999f15455f48 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -1431,13 +1431,8 @@ static int hsw_mm_switch(struct i915_hw_ppgtt *ppgtt,
>  {
>  	struct intel_engine_cs *engine = req->engine;
>  	u32 *cs;
> -	int ret;
>  
>  	/* NB: TLBs must be flushed and invalidated before a switch */
> -	ret = engine->emit_flush(req, EMIT_INVALIDATE | EMIT_FLUSH);

The pattern slightly changes as you dont get the flush on the first
switch.

But what is there to flush on first switch anyways.

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

> -	if (ret)
> -		return ret;
> -
>  	cs = intel_ring_begin(req, 6);
>  	if (IS_ERR(cs))
>  		return PTR_ERR(cs);
> @@ -1458,13 +1453,8 @@ static int gen7_mm_switch(struct i915_hw_ppgtt *ppgtt,
>  {
>  	struct intel_engine_cs *engine = req->engine;
>  	u32 *cs;
> -	int ret;
>  
>  	/* NB: TLBs must be flushed and invalidated before a switch */
> -	ret = engine->emit_flush(req, EMIT_INVALIDATE | EMIT_FLUSH);
> -	if (ret)
> -		return ret;
> -
>  	cs = intel_ring_begin(req, 6);
>  	if (IS_ERR(cs))
>  		return PTR_ERR(cs);
> @@ -1477,13 +1467,6 @@ static int gen7_mm_switch(struct i915_hw_ppgtt *ppgtt,
>  	*cs++ = MI_NOOP;
>  	intel_ring_advance(req, cs);
>  
> -	/* XXX: RCS is the only one to auto invalidate the TLBs? */
> -	if (engine->id != RCS) {
> -		ret = engine->emit_flush(req, EMIT_INVALIDATE | EMIT_FLUSH);
> -		if (ret)
> -			return ret;
> -	}
> -
>  	return 0;
>  }
>  
> -- 
> 2.11.0
>
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