TICK 与 CLOCK CYCLE 的区别

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Accurately Profiling Direct3D API Calls (Direct3D 9)(FROM DX HELP)

… …

BeginScene();

… …

// Start profiling

LARGE_INTEGER start, stop, freq;

QueryPerformanceCounter(&start);

SetTexture(...);

DrawPrimitive(D3DPT_TRIANGLELIST, 0, 1);

QueryPerformanceCounter(&stop);

stop.QuadPart -= start.QuadPart;

QueryPerformanceFrequency(&freq);

// Stop profiling

… …

EndScene();

Present();

Example 2: Custom Profiling Implementation with QPC

start and stop are two large integers that will hold the start and stop values returned by the high-performance timer. Notice that QueryPerformanceCounter(&start) is called just before IDirect3DDevice9::SetTexture and QueryPerformanceCounter(&stop) is called just after IDirect3DDevice9::DrawPrimitive. After getting the stop value, QueryPerformanceFrequency is called to return freq, which is the frequency of the high-resolution timer. In this hypothetical example, suppose you get the following results for start, stop, and freq:

Local Variable

Number of Ticks

start

1792998845094

stop

1792998845102

freq

3579545

You could convert these values to the number of cycles it takes to execute the API calls like this:

# ticks = (stop - start) = 1792998845102 - 1792998845094 = 8 ticks

# cycles = CPU speed * number of ticks / QPF

# 4568 = 2 GHz * 8 / 3,579,545

In other words, it takes about 4568 clock cycles to process IDirect3DDevice9::SetTexture and IDirect3DDevice9::DrawPrimitive on this 2 GHz machine. You could convert these values to the actual time it took to execute all the calls like this:

(stop - start)/ freq = elapsed time

8 ticks / 3,579,545 = 2.2E-6 seconds or between 2 and 3 microseconds.

需要清楚：

TICK，滴答，计算机的计时器的单位。

Hz，CLOCK CYCLE，CPU的时钟周期的单位。

QueryPerformanceFrequency()取出的TICK数是1秒钟内计算机计时器的滴答数。这个数值通常来自8253计时芯片。

2 GHz是1秒钟内CPU的时钟周期数。显然这个数据来自CPU。

在一个TICK里，计算机通过CPU要做（开、关开关）许多次。所以通常一秒钟时间里，CPU的CLOCK CYCLE都会比TICK大很多，这样在一个TICK里才可以让CPU跑很多个CLOCK CYCLE，完成很多操作。