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Date: Thu, 29 Jan 2015 22:51:22 -0500
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Subject: Re: svn commit: r277900 - head/sys/x86/x86
From: Ryan Stone <rysto32@gmail.com>
To: John Baldwin <jhb@freebsd.org>
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On Thu, Jan 29, 2015 at 3:45 PM, John Baldwin <jhb@freebsd.org> wrote:
> Also, note that we always use the TSC as the cpu ticker, even if it is not the
> timecounter.  Thus, if C2+ is enabled on the systems, the kernel idle threads
> will have an artificially low runtime since their idle time is not properly
> accounted for.  This does not affect any other threads as only the idle
> threads "run" while the CPU is in C2+ with the TSC effectively paused.  The
> new default means that the idle threads will now have the proper runtime,
> however.

However in a VM environment this means that runtimes for all threads
can be very wrong (regardless of whether we enter C2 or lower or not).
I have a coworker looking at using kvmclock in preference to TSC for
the cpu ticker when the kvmclock is available.