Hi,
I'm using the perf_event_open() syscall with the cycle event.
Here is a description of the argument I give to perf_event_open:
"attr": {
"type": "PERF_TYPE_HARDWARE",
"config": "PERF_COUNT_HW_CPU_CYCLES",
"sample_freq": 499,
"exclude_idle": true,
"exclude_host": true,
"freq": true,
"wakeup_events": 1,
"sample_type": [
"PERF_SAMPLE_IP",
"PERF_SAMPLE_CPU",
"PERF_SAMPLE_TIME"
]
}
While most of the samples I see have misc event of
PERF_RECORD_MISC_GUEST_KERNEL or PERF_RECORD_MISC_GUEST_USER, I still
see a very small amount of samples with PERF_RECORD_MISC_KERNEL
(1280/345161=0.38%).
I can see that the kernel is instructing the hardware to halt only inside guest
E.g., perf_event_intel.c:
cpuc->intel_ctrl_guest_mask |= (1ull << hwc->idx);
and then
wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL,
x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_guest_mask);
but I'm not sure if indeed the hardware PMUs guarantee never to
interrupt CPU when not in guest mode.
Is it expected? Is it a bug in my code?
(if needed, I can post the code that recreates this scenario).
Here is an example output, including all kind of samples, last line is
the MISC_KERNEL sample that shouldn't be there due to exclude_host in
perf_event_attr:
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_KERNEL","sample":{"ip":"ffffe8ff09853041","time":21195311625103,"cpu":3}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_KERNEL","sample":{"ip":"ffffe8ff0cbcfc60","time":21195312545321,"cpu":1}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_KERNEL","sample":{"ip":"ffffe8ff000107d4","time":21195313326630,"cpu":3}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_KERNEL","sample":{"ip":"ffffe8ff000698cb","time":21195314604935,"cpu":1}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_KERNEL","sample":{"ip":"ffffe8ff094e5ef0","time":21195315062329,"cpu":3}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_KERNEL","sample":{"ip":"ffffe8ff0006fd51","time":21195316464065,"cpu":1}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_KERNEL","sample":{"ip":"ffffe8ff000107c0","time":21195316880401,"cpu":3}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_USER","sample":{"ip":"416010","time":21195318316122,"cpu":1}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_GUEST_KERNEL","sample":{"ip":"ffffe8ff00003201","time":21195318703803,"cpu":3}}
{"type":"PERF_RECORD_SAMPLE","misc":"PERF_RECORD_MISC_KERNEL","sample":{"ip":"ffffffffa083cf54","time":21195320183609,"cpu":1}}
Thanks,
Elazar
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