linux-kernel - Re: [PATCH 4/6] drm/i915/gt: Only invalidate TLBs exposed to user manipulation

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Date:   Thu, 16 Jun 2022 08:33:24 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Chris Wilson <chris.p.wilson@...el.com>,
        Fei Yang <fei.yang@...el.com>,
        Thomas Hellstrom <thomas.hellstrom@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Airlie <airlied@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, mauro.chehab@...ux.intel.com,
        Andi Shyti <andi.shyti@...ux.intel.com>,
        stable@...r.kernel.org,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>
Subject: Re: [PATCH 4/6] drm/i915/gt: Only invalidate TLBs exposed to user
 manipulation


On 15/06/2022 16:27, Mauro Carvalho Chehab wrote:
> From: Chris Wilson <chris.p.wilson@...el.com>
> 
> Don't flush TLBs when the buffer is only used in the GGTT under full
> control of the kernel, as there's no risk of of concurrent access
> and stale access from prefetch.
> 
> We only need to invalidate the TLB if they are accessible by the user.
> 
> Fixes: 7938d61591d3 ("drm/i915: Flush TLBs before releasing backing store")

Same question as against the other patch - fix or optimisation?

Regards,

Tvrtko

> Signed-off-by: Chris Wilson <chris.p.wilson@...el.com>
> Cc: Fei Yang <fei.yang@...el.com>
> Cc: Andi Shyti <andi.shyti@...ux.intel.com>
> Cc: stable@...r.kernel.org
> Acked-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@...nel.org>
> ---
> 
> See [PATCH 0/6] at: https://lore.kernel.org/all/cover.1655306128.git.mchehab@kernel.org/
> 
>   drivers/gpu/drm/i915/i915_vma.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index 0bffb70b3c5f..7989986161e8 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -537,7 +537,8 @@ int i915_vma_bind(struct i915_vma *vma,
>   				   bind_flags);
>   	}
>   
> -	set_bit(I915_BO_WAS_BOUND_BIT, &vma->obj->flags);
> +	if (bind_flags & I915_VMA_LOCAL_BIND)
> +		set_bit(I915_BO_WAS_BOUND_BIT, &vma->obj->flags);
>   
>   	atomic_or(bind_flags, &vma->flags);
>   	return 0;