qemu kvm:如何获取性能监视中断? [英] qemu kvm: how to get permformance monitoring interrupt?

问题描述

我在OS内核中编写了一些函数，以在指令计数器溢出时发出性能监视中断(PMI).它在我的机器(Intel酷睿i5)上运行良好.但是当我使用

I write some function in my OS kernel to issue the performance monitoring interrupt (PMI) on instructions counter overflow. It works well on my machine (Intel core i5). But when I run it on qemu using

qemu-system-x86_64 -enable-kvm -cpu host -m 256 -serial mon:stdio -cdrom var/run/hypervisor.iso

qemu-system-x86_64 -enable-kvm -cpu host -m 256 -serial mon:stdio -cdrom var/run/hypervisor.iso

该中断不会触发. 有什么我想念的吗? 是否需要任何特殊配置才能在Qemu上触发PMI? 我记得指令计数在qemu中很好用. msr注册以激活PMI

the interrupt does never fire. Is there anything I am missing? Does it require any special configuration to get the PMI fired on qemu? I recall that instruction counting works well in qemu. msr registers to activate PMI

Msr::write(Msr::MSR_PERF_GLOBAL_CTRL, 0x700000003);
Msr::write(Msr::MSR_PERF_FIXED_CTRL, 0xa);
Msr::write(Msr::IA32_PERFEVTSEL0, 0x004100c5);

为PMI编写0x1000指令

Program the PMI for 0x1000 instructions

Msr::write(Msr::IA32_PERF_GLOBAL_OVF_CTRL, 1ull << 32);
Msr::write(Msr::MSR_PERF_FIXED_CTR0, 0xFFFFEFFF | 0xFFFF00000000);

推荐答案

从讨论中此处，您可以看到kvm仅在写入PERF_FIXED_CTR_CTRL(0x38d)时才更新虚拟计数器.

From the discussion here, you can read that kvm updates the virtual counter only when you write into PERF_FIXED_CTR_CTRL (0x38d).

因此，要获得pmi，最好在设置计数器值之后，将该寄存器设置在最后一个位置.

So, to get the pmi, you better set this register at last position, after setting the counter value of course.

为了完整起见，必须按以下顺序发布说明:

For the sake of completeness, instructions must be issued in this order:

; set counter value.
mov edx, 0xffff
mov eax, 0xffff0000
mov ecx, 0x309
wrmsr

; set counting mode
xor edx, edx
mov eax, 0xa
mov ecx, 0x38d
wrmsr

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