Re: [PATCH] drm/i915/vgpu: Neuter forcewakes for VGPU more thouroughly

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

Hi,

On 13/03/2017 09:37, Zhenyu Wang wrote:
> On 2017.03.13 09:26:26 +0000, Tvrtko Ursulin wrote:
>>
>> On 10/03/2017 10:09, Chris Wilson wrote:
>>> On Fri, Mar 10, 2017 at 09:57:47AM +0000, Tvrtko Ursulin wrote:
>>>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>
>>>> If we avoid initializing forcewake domains when running as
>>>> a guest, and also use gen2 mmio accessors in that case, we
>>>> can avoid the timer traffic and any looping through the
>>>> forcewake code which is currently just so it can end up in
>>>> the no-op forcewake implementation.
>>>>
>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>> Cc: Weinan Li <weinan.z.li@intel.com>
>>>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>>>> ---
>>>>  drivers/gpu/drm/i915/intel_uncore.c | 76 +++++++++++++------------------------
>>>>  1 file changed, 27 insertions(+), 49 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
>>>> index 71b9b387ad04..09f5f02d7901 100644
>>>> --- a/drivers/gpu/drm/i915/intel_uncore.c
>>>> +++ b/drivers/gpu/drm/i915/intel_uncore.c
>>>> @@ -138,13 +138,6 @@ fw_domains_put(struct drm_i915_private *dev_priv, enum forcewake_domains fw_doma
>>>>  }
>>>>
>>>>  static void
>>>> -vgpu_fw_domains_nop(struct drm_i915_private *dev_priv,
>>>> -		    enum forcewake_domains fw_domains)
>>>> -{
>>>> -	/* Guest driver doesn't need to takes care forcewake. */
>>>> -}
>>>> -
>>>> -static void
>>>>  fw_domains_posting_read(struct drm_i915_private *dev_priv)
>>>>  {
>>>>  	struct intel_uncore_forcewake_domain *d;
>>>> @@ -1187,7 +1180,7 @@ static void fw_domain_init(struct drm_i915_private *dev_priv,
>>>>
>>>>  static void intel_uncore_fw_domains_init(struct drm_i915_private *dev_priv)
>>>>  {
>>>> -	if (INTEL_INFO(dev_priv)->gen <= 5)
>>>> +	if (INTEL_GEN(dev_priv) <= 5 || intel_vgpu_active(dev_priv))
>>>
>>> Make these separate ifs, they aren't semantically related so be verbose.
>>>
>>>>  		return;
>>>>
>>>>  	if (IS_GEN9(dev_priv)) {
>>>> @@ -1273,11 +1266,6 @@ static void intel_uncore_fw_domains_init(struct drm_i915_private *dev_priv)
>>>>  			       FORCEWAKE, FORCEWAKE_ACK);
>>>>  	}
>>>>
>>>> -	if (intel_vgpu_active(dev_priv)) {
>>>> -		dev_priv->uncore.funcs.force_wake_get = vgpu_fw_domains_nop;
>>>> -		dev_priv->uncore.funcs.force_wake_put = vgpu_fw_domains_nop;
>>>> -	}
>>>> -
>>>>  	/* All future platforms are expected to require complex power gating */
>>>>  	WARN_ON(dev_priv->uncore.fw_domains == 0);
>>>>  }
>>>> @@ -1327,22 +1315,22 @@ void intel_uncore_init(struct drm_i915_private *dev_priv)
>>>>  	dev_priv->uncore.pmic_bus_access_nb.notifier_call =
>>>>  		i915_pmic_bus_access_notifier;
>>>>
>>>> -	switch (INTEL_INFO(dev_priv)->gen) {
>>>> -	default:
>>>> -	case 9:
>>>> -		ASSIGN_FW_DOMAINS_TABLE(__gen9_fw_ranges);
>>>> -		ASSIGN_WRITE_MMIO_VFUNCS(fwtable);
>>>> -		ASSIGN_READ_MMIO_VFUNCS(fwtable);
>>>> -		if (HAS_DECOUPLED_MMIO(dev_priv)) {
>>>> -			dev_priv->uncore.funcs.mmio_readl =
>>>> -						gen9_decoupled_read32;
>>>> -			dev_priv->uncore.funcs.mmio_readq =
>>>> -						gen9_decoupled_read64;
>>>> -			dev_priv->uncore.funcs.mmio_writel =
>>>> -						gen9_decoupled_write32;
>>>> +	if (IS_GEN(dev_priv, 2, 4) || intel_vgpu_active(dev_priv)) {
>>>
>>> Ok, this doesn't look too bad.
>>>
>>> Do the gvt-g hosts in CI now provide coverage for us of vgpu paths?
>>
>> No idea.
>>
>> Adding Zhenyu. So this patch avoids burning CPU cycles in guests and
>> scheduling timers when all of that ends up in the dummy/no-op forcewake
>> implementation.
>>
>> If interesting to you, would it be easy for you to test it or how should we
>> proceed?
>>
>
> Patch looks fine to me. I can apply it for our QA testing if required.

Were you perhaps able to smoke test this one?

Regards,

Tvrtko

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