如何在过程中配置和采样英特尔性能计数器

问题描述

简而言之，我正在尝试在用户级基准测试流程(伪代码，假设x86_64和UNIX系统)中实现以下目标:

In a nutshell, I'm trying to achieve the following inside a userland benchmark process (pseudo-code, assuming x86_64 and a UNIX system):

results[] = ...
for (iteration = 0; iteration < num_iterations; iteration++) {
    pctr_start = sample_pctr();
    the_benchmark();
    pctr_stop = sample_pctr();
    results[iteration] = pctr_stop - pctr_start;
}

FWIW，我正在考虑使用的性能计数器是CPU_CLK_UNHALTED.THREAD_ALL，用于读取独立于时钟频率变化的核心周期数(在 PAPI 建立在perf之上，因此很可能继承了上述问题.

编写内核模块-太费力了，容易出错.

• Perf tools for Linux. Seems to be geared up for sampling over the whole lifetime of a process, not within a process as specific points (before and after each iteration).
• Use perf syscalls directly (i.e. perf_event_open). Looks like the counter value will only update periodically (using a sample rate) or after the counter exceeds a threshold. I need the counter value precisely at the moment I ask. This is why RDPMC seemed so attractive. I imagine that sampling frequently will itself skew the performance counter readings.
• PAPI builds on perf, so probably inherits the above problem.
• Write a kernel module -- too much effort, too error prone.

理想情况下，我想要一个可以在OpenBSD和Linux上运行的解决方案，但是我认为这是一个很高的要求.也许目前仅适用于Linux.

Ideally I would like a solution which works on OpenBSD and Linux, but somehow I think that is a tall order. Perhaps just for Linux for now.

我们非常感谢您的帮助.谢谢.

Any help is most appreciated. Thanks.

我刚刚找到了 Linux msr设备节点，这可能就足够了.如果出现更好的答案，我将保留该问题.

I just found the Linux msr device node, which would probably suffice. I'll leave the question up in case a better answer shows up.

推荐答案

似乎最好的方法-至少对于Linux-是使用 msr设备节点.

It seems the best way -- for Linux at least -- is to use the msr device node.

您只需打开设备节点，查找所需的MSR地址，然后读取或写入8个字节即可.

You simply open a device node, seek to the address of the MSR required, and read or write 8 bytes.

OpenBSD更加困难，因为(在编写本文时)没有用户空间代理到MSR.因此，您需要手动编写内核模块或实现sysctl.

OpenBSD is harder, since (at the time of writing) there is no user-space proxy to the MSRs. So you would need to write a kernel module or implement a sysctl by hand.

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