Description

The OS calls DxgkDdiUpdateCurrentValuesFromCpu to update the CurrentValue of a batch of native fences from the CPU.

Parameters

pUpdateCurrentValuesFromCpu

[in] Pointer to a DXGKARG_UPDATECURRENTVALUESFROMCPU structure that contains the current values to update.

Return value

Remarks

This DDI is used to support the existing "signal fence from CPU" API semantics. Instead of Dxgkrnl writing a new CurrentValue, the driver is asked to write to CurrentValue in order to give drivers an opportunity to insert any required pre-write synchronization/barriers. The OS synchronizes CPU-side updates and guarantees that the most up to date value is available to DxgkDdiUpdateCurrentValuesFromCpu. After updating CurrentValue, the driver must trigger the GPU to unblock hardware queues that were waiting on this fence and got unblocked with the update to CurrentValue.

In a nutshell the steps to be followed by the driver are:

for i = 1 : NumFences
  1. Insert pre-write memory barrier if required
  2. write new value to CurrentValueCpuVa
  3. trigger GPU to unblock any HwQueues that got unblocked by the updated CurrentValue
end

The OS only guarantees that the CurrentValueKernelCpuVa pointer is valid for the duration of this DDI call, and not before or after it. Hence, KMD must never cache this pointer for use elsewhere.

For more information about native GPU fences, see Native GPU fence objects.

See also

DXGKARG_UPDATECURRENTVALUESFROMCPU