AtomicMin

Applicability

Function Usage

Performs atomic minimization on the specified global memory address.

Prototype

1
2

template <typename T>
__aicore__ inline T AtomicMin(__gm__ T *address, T value)

Parameters

Returns

Data before the atomic operation is performed on the global memory address.

Constraints

The atomic operation involves scalar computation. If the Scalar Unit and DMA unit (MTE2/MTE3) have data dependencies during global memory read and write, you need to insert synchronization as needed.

Example

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13

// Pass the address of the global data to initialize dstGlobal and dstLocal.
dstGlobal.SetGlobalBuffer(reinterpret_cast<__gm__ T *>(dstGm), dataSize);

LocalTensor<T> dstLocal = inQueueX.AllocTensor<T>();
int32_t value = 0;
int32_t a = AscendC::AtomicMin(reinterpret_cast<__gm__ int32_t *>(dstGm), value);
// The movement operation can be performed only after the atomic operation is complete. There are data dependencies.
event_t eventIdSToMte2 = static_cast<event_t>(GetTPipePtr()->AllocEventID<HardEvent::S_MTE2>());
// Manually insert the MTE2 wait for Scalar Unit synchronization.
SetFlag<HardEvent::S_MTE2>(eventIdSToMte2);
WaitFlag<HardEvent::S_MTE2>(eventIdSToMte2);
DataCopy(dstLocal, dstGlobal, dataSize);
// ...

Assume that the preceding function is executed on three cores, and core 1, core 2, and core 3 are scheduled in sequence. The result example is as follows:

Original global memory data dst: [1,1,1,1,1,...,1] 
Core 1:
Global memory data dst after atomic computation: [0,1,1,1,1,...,1] 
Return value a: 1
Core 2:
Global memory data dst after atomic computation: [0,1,1,1,1,...,1] 
Return value a: 0
Core 3:
Global memory data dst after atomic computation: [0,1,1,1,1,...,1] 
Return value a: 0