Question

How do I determine the CPE of a program? For example, I have this assembly code for a loop:

# inner4: data_t = float
# udata in %rbx, vdata in %rax, limit in %rcx,
# i in %rdx, sum in %xmm1
1 .L87:                                   # loop:
2   movss  (%rbx,%rdx,4), %xmm0           #  Get udata[i]
3   mulss  (%rax,%rdx,4), %xmm0           #  Multiply by vdata[i]
4   addss  %xmm0, %xmm1                   #  Add to sum
5   addq  $1, %rdx                        #  Increment i
6   cmpq  %rcx, %rdx                      #  Compare i:limit
7   jl .L87                               #  If <, goto loop

我必须找到由使用数据类型浮动的关键性途径确定的低限值。我认为,关键的道路将指最缓慢的道路,因此,方案必须执行训令,因为这需要时间最长的锁定周期。

However, there doesn t seem to be any clear way to determine the CPE. If one instruction takes two clock cycles, and another takes one, can the latter start after the first clock cycle of the former? Any help would be appreciated. Thanks

Answer 1

如果你想要知道它需要多长时间,你就应该衡量。大约10^10次休息时间,需要时间,乘以24小时的频率。您的周期总数为10^10,以获得每处夜总会的数量。

对执行时间的理论预测几乎是never的正确(以及大部分时间到低),因为影响很多,决定了速度:

Pipelining (there can be easily about 20 stages in the pipeline)
Superscalar execution (up to 5 instructions in parallel, cmp and jl may be fused)
Decoding to µOps and reordering
The latencies of Caches or Memory
The throughput of the instructions (are there enough executions ports free)
The latencies of the instructions
Bank conflicts, aliasing issues and more esoteric stuff

视万国邮联而定,并且提供所有触角的记忆,我认为,每轮休息至少需要3个24小时的循环,因为最长的依赖链是3个因素。更慢的CPU(muls或adds指示所需时间增加。

如果你实际上有意加快该守则的速度,而不仅仅是一些理论性意见,那么你就应当把它作为工具。你可以把4-8级的系数提高业绩。

.L87:                               # loop:
vmovdqa (%rbx,%rdx,4), %ymm0        #  Get udata[i]..udata[i+7]
vmulps  (%rax,%rdx,4), %ymm0, %ymm0 #  Multiply by vdata[i]..vdata[i+7]
vaddps  %ymm0, %ymm1, %ymm1         #  Add to sum
addq    $8, %rdx                    #  Increment i
cmpq    %rcx, %rdx                  #  Compare i:limit
jl .L87                             #  If <, goto loop

在此之后,你需要横向增加所有8个要素,当然确保一致性是32个,反之,在8个层面。

Answer 2

如果你重新经营一个英特尔邮联,你可以找到一些关于各邮联的指令性和投入的良好文件。这里指的是:

Intel® 64 and IA-32 Architectures Optimization Reference Manual

友情链接