Re: [Intel-gfx] [PATCH] drm/i915/guc/slpc: Use non-blocking H2G for waitboost

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 16 May 2022, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> On Sat, 14 May 2022, Vinay Belgaumkar <vinay.belgaumkar@intel.com> wrote:
>> SLPC min/max frequency updates require H2G calls. We are seeing
>> timeouts when GuC channel is backed up and it is unable to respond
>> in a timely fashion causing warnings and affecting CI.
>>
>> This is seen when waitboosting happens during a stress test.
>> this patch updates the waitboost path to use a non-blocking
>> H2G call instead, which returns as soon as the message is
>> successfully transmitted.
>>
>> v2: Use drm_notice to report any errors that might occur while
>> sending the waitboost H2G request (Tvrtko)
>>
>> Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
>> ---
>>  drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c | 44 +++++++++++++++++----
>>  1 file changed, 36 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
>> index 1db833da42df..e5e869c96262 100644
>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_slpc.c
>> @@ -98,6 +98,30 @@ static u32 slpc_get_state(struct intel_guc_slpc *slpc)
>>  	return data->header.global_state;
>>  }
>>  
>> +static int guc_action_slpc_set_param_nb(struct intel_guc *guc, u8 id, u32 value)
>> +{
>> +	u32 request[] = {
>
> static const

*sigh*

-ENOCOFFEE, please ignore the mail.

BR,
Jani.


>
>> +		GUC_ACTION_HOST2GUC_PC_SLPC_REQUEST,
>> +		SLPC_EVENT(SLPC_EVENT_PARAMETER_SET, 2),
>> +		id,
>> +		value,
>> +	};
>> +	int ret;
>> +
>> +	ret = intel_guc_send_nb(guc, request, ARRAY_SIZE(request), 0);
>> +
>> +	return ret > 0 ? -EPROTO : ret;
>> +}
>> +
>> +static int slpc_set_param_nb(struct intel_guc_slpc *slpc, u8 id, u32 value)
>> +{
>> +	struct intel_guc *guc = slpc_to_guc(slpc);
>> +
>> +	GEM_BUG_ON(id >= SLPC_MAX_PARAM);
>> +
>> +	return guc_action_slpc_set_param_nb(guc, id, value);
>> +}
>> +
>>  static int guc_action_slpc_set_param(struct intel_guc *guc, u8 id, u32 value)
>>  {
>>  	u32 request[] = {
>
> Ditto here, and the whole gt/uc directory seems to have tons of these
> u32 action/request array variables on stack, with the required
> initialization, that could be in rodata.
>
> Please fix all of them.
>
> BR,
> Jani.
>
>> @@ -208,12 +232,10 @@ static int slpc_force_min_freq(struct intel_guc_slpc *slpc, u32 freq)
>>  	 */
>>  
>>  	with_intel_runtime_pm(&i915->runtime_pm, wakeref) {
>> -		ret = slpc_set_param(slpc,
>> -				     SLPC_PARAM_GLOBAL_MIN_GT_UNSLICE_FREQ_MHZ,
>> -				     freq);
>> -		if (ret)
>> -			i915_probe_error(i915, "Unable to force min freq to %u: %d",
>> -					 freq, ret);
>> +		/* Non-blocking request will avoid stalls */
>> +		ret = slpc_set_param_nb(slpc,
>> +					SLPC_PARAM_GLOBAL_MIN_GT_UNSLICE_FREQ_MHZ,
>> +					freq);
>>  	}
>>  
>>  	return ret;
>> @@ -222,6 +244,8 @@ static int slpc_force_min_freq(struct intel_guc_slpc *slpc, u32 freq)
>>  static void slpc_boost_work(struct work_struct *work)
>>  {
>>  	struct intel_guc_slpc *slpc = container_of(work, typeof(*slpc), boost_work);
>> +	struct drm_i915_private *i915 = slpc_to_i915(slpc);
>> +	int err;
>>  
>>  	/*
>>  	 * Raise min freq to boost. It's possible that
>> @@ -231,8 +255,12 @@ static void slpc_boost_work(struct work_struct *work)
>>  	 */
>>  	mutex_lock(&slpc->lock);
>>  	if (atomic_read(&slpc->num_waiters)) {
>> -		slpc_force_min_freq(slpc, slpc->boost_freq);
>> -		slpc->num_boosts++;
>> +		err = slpc_force_min_freq(slpc, slpc->boost_freq);
>> +		if (!err)
>> +			slpc->num_boosts++;
>> +		else
>> +			drm_notice(&i915->drm, "Failed to send waitboost request (%d)\n",
>> +				   err);
>>  	}
>>  	mutex_unlock(&slpc->lock);
>>  }

-- 
Jani Nikula, Intel Open Source Graphics Center