Behavior of base::ThreadTicks and blocking IO

[Charles Harrison]

Hello scheduler-dev@,

dcheng pointed me your way with this question. I was wondering if base::ThreadTicks counts the time a thread is doing blocking IO? e.g. if I read() a large file, will ThreadTicks count that time?

My sense from reading the documentation from CLOCK_THREAD_CPUTIME_ID on linux is that no, it will not. Can you confirm?

Regardless of the answer, I would be happy to improve the documentation in time.h. Thanks!

[Wez]

Normally thread-time is time spent scheduled on the CPU, so doesn't include time spent blocked on I/O, ready-to-run, etc.

ThreadTicks documentation says:

// `ThreadTicks` will "stand still" whenever the thread has been de-scheduled

// by the operating system.

so I think you can assume that that is an invariant across the platforms Chromium supports.

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[Charlie Harrison]

Thanks Wez!

[Wez]

No problem!  If you'd like to improve the documentation to make that expectation more obvious, feel free to send me a CL to review :)

[Charles Harrison]

Yes I will, I think my gap in knowledge is a precise understanding of what it means for a thread to be "scheduled" on the CPU and how that relates to IO. I will think about how to convey this in the documentation.