On Fri, Jan 13, 2017 at 08:26:04AM +0800, Jia-Shiun Li wrote:
> Hi all,
> since 2 or 3 weeks ago, I noticed that my old Penryn-based Intel Pentium
> T4200 notebook lagged a lot. System time was running a lot slower,
> sometimes even looked like it freezed. Keystroke repeat rate was slow too.
> Since system time is slow, I tried to change timecounter from default TSC
> to HPET. And it resumed normal immediately.
Please show the output of sysctl kern.timecounter and kern.eventtimer.
I suspect that you changed eventtimer and not timecounter.

> The same world binary works fine on other Ivybridge and Haswell desktops,
> so I assume this may be related to CPU or mainboard generations.
> version is
> FreeBSD jsli-nb 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r311687: Mon Jan  9
> 04:07:27 CST 2017
> jsli@4cbsd:/personal/freebsd/obj/x64/personal/freebsd/fbsdsrc/sys/MINIMAL-NODEBUG
> amd64
> and CPU is
> CPU: Pentium(R) Dual-Core CPU       T4200  @ 2.00GHz (1995.04-MHz K8-class
> CPU)
>   Origin="GenuineIntel"  Id=0x1067a  Family=0x6  Model=0x17  Stepping=10
>   AMD Features=0x20100800<SYSCALL,NX,LM>
>   AMD Features2=0x1<LAHF>
>   TSC: P-state invariant, performance statistics
> Tested similar OS rev on another Intel Core 2 Duo E7400 Wolfdale (the same
> generation as the Pentium T4200). The same lag also happens on it.
> BTW on both system, cpuX:timer interrupts do not fire at all and count
> remains 0.
It is known that LAPIC is shut down in C2 and deeper CPU sleep states on
Core2.  FreeBSD 11 (and HEAD) started using MWAIT and requesting deep
wait states from BIOS.  If the configuration uses LAPIC and deep sleeps
are enabled, eventtimers do not work reliably.

Default configuration should strongly prefer HPET eventtimer over LAPIC for 
machines which do not have LAPIC armed in Cx states, see r309189.  If you
do not have any customizations of eventtimer selection, then please provide
verbose dmesg from your boot.

If you prefer to not use deep Cx and MWAIT, set loader tunable
debug.acpi.disabled to include word "mwait", see acpi(4).  You can check
that this worked by looking at sysctl dev.cpu.N output.
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