TSC as timecounter makes system lag

[Konstantin Belousov]

On Fri, Feb 24, 2017 at 12:15:26PM +0800, Jia-Shiun Li wrote:
> On Fri, Feb 24, 2017 at 12:55 AM, John Baldwin <jhb at freebsd.org> wrote:
> 
> > On Thursday, February 23, 2017 11:04:58 PM Jia-Shiun Li wrote:
> > >
> > >
> > > 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?
> >
> > We don't actually need cpu_deepest_sleep.  We could just set C2STOP always.
> > It doesn't hurt to have the flag set if the system only supports C1 except
> > that you get the printf in a verbose boot.
> >
> > Try this slight variation of Konstantin's patch.  If this works we can
> > remove
> > cpu_deepest_sleep entirely as a followup since it will no longer be used:
> >
> > Index: tsc.c
> > ===================================================================
> > --- tsc.c       (revision 314113)
> > +++ tsc.c       (working copy)
> > @@ -542,9 +542,11 @@ init_TSC_tc(void)
> >          * result incorrect runtimes for kernel idle threads (but not
> >          * for any non-idle threads).
> >          */
> > -       if (cpu_deepest_sleep >= 2 && cpu_vendor_id == CPU_VENDOR_INTEL &&
> > +       if (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");
> >         }
> >
> 
> Tested working on E7400 against r313909. And changing timecounter from/to
> TSC
> correctly enables/disables C2.
> 
> The latter part cpu_disable_c2_sleep++ is not needed. When
> init_TSC_tc() got called timecounter is not yet tsc_timecounter.
> inittimecounter() later will do the work calling tc_windup().
> 

You mean, just this
-       if (cpu_deepest_sleep >= 2 && cpu_vendor_id == CPU_VENDOR_INTEL &&
+       if (cpu_vendor_id == CPU_VENDOR_INTEL &&
is enough to fix the issue ?  If yes, we can remove the cpu_deepest_sleep
variable.  This is John' observation, I think he would prefer to prepare
the patch.