bperf: Avoid "time going back" in per thread reader #380
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Summary: We use rdtsc to estimate enabled and running time. However, kernel occasionally adjusts the algorithm of tsc based timer. Therefore, extra care is need to avoid "time going back" issue. Please refer to the comment before kernel function ktime_get_mono_fast_ns() for more information. Here, we make time_after_offset_update 0.1% smaller. So that the time never goes back. This is not an issue for time_enabled and time_running, as they are only used adjust PMC reading. However, cpuTime may show some spikes when we adjust the time forward. Differential Revision: D75930645
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Summary:
We use rdtsc to estimate enabled and running time. However,
kernel occasionally adjusts the algorithm of tsc based timer.
Therefore, extra care is need to avoid "time going back" issue.
Please refer to the comment before kernel function
ktime_get_mono_fast_ns() for more information.
Here, we make time_after_offset_update 0.1% smaller. So that
the time never goes back. This is not an issue for time_enabled
and time_running, as they are only used adjust PMC reading.
However, cpuTime may show some spikes when we adjust the time
forward.
Differential Revision: D75930645