linux-kernel - Re: [PATCH v2 05/21] drm/i915/gt: Skip TLB invalidations once wedged

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Message-ID: <d51882e0-6864-7a49-ae16-f7213dc716c4@linux.intel.com>
Date:   Mon, 18 Jul 2022 14:45:22 +0100
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Chris Wilson <chris.p.wilson@...el.com>,
        Andi Shyti <andi.shyti@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Daniele Ceraolo Spurio <daniele.ceraolospurio@...el.com>,
        Dave Airlie <airlied@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Matt Roper <matthew.d.roper@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Fei Yang <fei.yang@...el.com>,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>
Subject: Re: [PATCH v2 05/21] drm/i915/gt: Skip TLB invalidations once wedged


On 14/07/2022 13:06, Mauro Carvalho Chehab wrote:
> From: Chris Wilson <chris.p.wilson@...el.com>
> 
> Skip all further TLB invalidations once the device is wedged and
> had been reset, as, on such cases, it can no longer process instructions
> on the GPU and the user no longer has access to the TLB's in each engine.
> 
> That helps to reduce the performance regression introduced by TLB
> invalidate logic.
> 
> Cc: stable@...r.kernel.org
> Fixes: 7938d61591d3 ("drm/i915: Flush TLBs before releasing backing store")

Is the claim of a performance regression this solved based on a wedged 
GPU which does not work any more to the extend where mmio tlb 
invalidation requests keep timing out? If so please clarify in the 
commit text and then it looks good to me. Even if it is IMO a very 
borderline situation to declare something a fix.

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>
> Acked-by: Thomas Hellström <thomas.hellstrom@...ux.intel.com>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@...nel.org>
> ---
> 
> To avoid mailbombing on a large number of people, only mailing lists were C/C on the cover.
> See [PATCH v2 00/21] at: https://lore.kernel.org/all/cover.1657800199.git.mchehab@kernel.org/
> 
>   drivers/gpu/drm/i915/gt/intel_gt.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
> index 1d84418e8676..5c55a90672f4 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt.c
> @@ -934,6 +934,9 @@ void intel_gt_invalidate_tlbs(struct intel_gt *gt)
>   	if (I915_SELFTEST_ONLY(gt->awake == -ENODEV))
>   		return;
>   
> +	if (intel_gt_is_wedged(gt))
> +		return;
> +
>   	if (GRAPHICS_VER(i915) == 12) {
>   		regs = gen12_regs;
>   		num = ARRAY_SIZE(gen12_regs);