Re: TSC as timecounter makes system lag

On Thu, Feb 23, 2017 at 6:08 PM, Konstantin Belousov <kostikbel_at_gmail.com>
wrote:

>
> This is a useful analysis.
>
> Yes, I think that there is an init ordering issue. Note that
> cpu_disable_c2_sleep is only changed in tc_windup() when timecounter
> is changed. If existing and already engadged timecounter suddenly gets
> TC_FLAG_C2STOP set, tc_windup() ignores the flag.  And with the early
> AP startup, tsc seems to be set as timecounter too early.
>
> Just moving order of init_TSC_tc() would not help, since tsc checks smp
> consistency, which requires started APs.  Try this for now, but might
> be John has better idea how to handle the issue.  You might need to add
> some extern declarations for the patch to compile.
>
> diff --git a/sys/x86/x86/tsc.c b/sys/x86/x86/tsc.c
> index 3f36fbd9f8a..f8e33069c70 100644
> --- a/sys/x86/x86/tsc.c
> +++ b/sys/x86/x86/tsc.c
> _at__at_ -545,6 +545,8 _at__at_ init_TSC_tc(void)
>         if (cpu_deepest_sleep >= 2 && cpu_vendor_id == CPU_VENDOR_INTEL &&
>             (amd_pminfo & AMDPM_TSC_INVARIANT) == 0) {
>                 tsc_timecounter.tc_flags |= TC_FLAGS_C2STOP;
> +               if (timecounter == &tsc_timecounter)
> +                       cpu_disable_c2_sleep++;
>                 if (bootverbose)
>                         printf("TSC timecounter disables C2 and C3.\n");
>         }
>


This does not work.

I added a printf before the outer if clause, and it says

init_TSC_tc:546: deepest 00000000 vendor 00008086 amd_pminfo 00000000

full boot dmesg attached. Looks init_TSC_tc() is called too early before
acpi_cpu_attach() initializing cpu_deepest_sleep. Maybe it should be put
after
driver initialization, since it depends on probed ACPI C states?

-Jia-Shiun.