Re: [PATCH] Use UEFI Time Service to calibrate TSC

[Michael Chang]

On Mon, Nov 09, 2015 at 10:29:55AM +0300, Andrei Borzenkov wrote:
> On Mon, Nov 9, 2015 at 10:07 AM, Michael Chang <address@hidden> wrote:
> > This patch tries to detect PIT timer is broken and use UEFI Time Service
> > to calibrate TSC.
> 
> Second try :)
> 
> https://lists.gnu.org/archive/html/grub-devel/2014-11/msg00079.html
> 
> Although I think that this one is acceptable - it is used as fallback
> only. Will it also catch the case when PIT is not present at all?

I think yes, actually this patch was tested and can fix the timeout
problem on hyper-v Generation 2 VMs with UEFI, which is known to ship
without PIT.

In addition to that, the linux kernel also calibrates the tsc via PIT as
default on x86.

http://lxr.free-electrons.com/source/arch/x86/kernel/tsc.c#L441

But with some sanity checks to detect the SMI storm interfering the
result and will fallback to other timer sources if the sanity check
fails. This patch is inspired by that one of that check with much more
restricted loopmin to "1" that's basically a insane condition. 

Thanks,
Michael

> 
> > ---
> >  grub-core/kern/i386/tsc.c |   33 +++++++++++++++++++++++++++++----
> >  1 files changed, 29 insertions(+), 4 deletions(-)
> >
> > diff --git a/grub-core/kern/i386/tsc.c b/grub-core/kern/i386/tsc.c
> > index bc441d0..bd24cea 100644
> > --- a/grub-core/kern/i386/tsc.c
> > +++ b/grub-core/kern/i386/tsc.c
> > @@ -29,6 +29,10 @@
> >  #include <grub/xen.h>
> >  #else
> >  #include <grub/i386/pit.h>
> > +#ifdef GRUB_MACHINE_EFI
> > +#include <grub/efi/efi.h>
> > +#include <grub/efi/api.h>
> > +#endif
> >  #endif
> >  #include <grub/cpu/io.h>
> >
> > @@ -72,7 +76,7 @@ grub_cpu_is_tsc_supported (void)
> >  }
> >
> >  static void
> > -grub_pit_wait (grub_uint16_t tics)
> > +grub_pit_wait (grub_uint16_t tics, int *is_started)
> >  {
> >    /* Disable timer2 gate and speaker.  */
> >    grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
> > @@ -90,8 +94,17 @@ grub_pit_wait (grub_uint16_t tics)
> >              | GRUB_PIT_SPK_TMR2,
> >               GRUB_PIT_SPEAKER_PORT);
> >
> > -  /* Wait.  */
> > -  while ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH) == 
> > 0x00);
> > +  if ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH))
> > +    {
> > +      /* The ticks have expired too fast to know the counting really 
> > started or not */
> > +      *is_started = 0;
> > +    }
> > +  else
> > +    {
> > +      *is_started = 1;
> > +      /* Wait.  */
> > +      while ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH) 
> > == 0x00);
> > +    }
> >
> >    /* Disable timer2 gate and speaker.  */
> >    grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
> > @@ -117,11 +130,23 @@ calibrate_tsc (void)
> >  {
> >    /* First calibrate the TSC rate (relative, not absolute time). */
> >    grub_uint64_t end_tsc;
> > +  int is_started;
> >
> >    tsc_boot_time = grub_get_tsc ();
> > -  grub_pit_wait (0xffff);
> > +  grub_pit_wait (0xffff, &is_started);
> >    end_tsc = grub_get_tsc ();
> >
> > +#ifdef GRUB_MACHINE_EFI
> > +  /* The PIT is broken as 55ms is too sufficent to any cpu to catch it */
> > +  if (!is_started)
> > +    {
> > +      /* Use EFI Time Service to calibrate TSC */
> > +      tsc_boot_time = grub_get_tsc ();
> > +      efi_call_1 (grub_efi_system_table->boot_services->stall, 54925);
> > +      end_tsc = grub_get_tsc ();
> > +    }
> > +#endif
> > +
> >    grub_tsc_rate = 0;
> >    if (end_tsc > tsc_boot_time)
> >      grub_tsc_rate = grub_divmod64 ((55ULL << 32), end_tsc - tsc_boot_time, 
> > 0);
> > --
> > 1.7.3.4
> >
> >
> > _______________________________________________
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> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/grub-devel
> 
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