Re: [PATCH] calibrate_tsc(): use the Stall() EFI boot service on GRUB_MACHINE_EFI

[Michael Chang]

On Mon, Nov 30, 2015 at 08:34:18PM +0300, Andrei Borzenkov wrote:
> 30.11.2015 19:50, Andrei Borzenkov пишет:
> > 30.11.2015 19:31, Vitaly Kuznetsov пишет:
> >> Andrei Borzenkov <address@hidden> writes:
> >>
> >>> 26.11.2014 11:59, Laszlo Ersek пишет:
> >>>> HyperV Gen2 virtual machines have no PIT; guest code should rely on UEFI
> >>>> services instead.
> >>>>
> >>>
> >>> Could you retest with current master? It now supports multiple methods
> >>> to calibrate TSC and should avoid PIT on UEFI systems.
> >>
> >> Unfortunately, current master (grub-2.02-beta2-561-g346a494) still
> >> doesn't work for me, timer keeps running like crazy on Gen2 Hyper-V VMs.
> >>
> > 
> > @Michael: I remember you tested version of Vladimir patch on Hyper-V?
> > Could you test current master?
> > 

I don't have access to Hyper-V either. My initial patch was tested on
Hyper-V from my colleage in Nuremburg. For Vladimir's patch I did tests
on my EFI machine and mostly intersted in pmtimer to function properly,
as that's new introduced timer to the patch .. 

> 
> 
>   if ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH)) {
>     ret = 1;
>     /* Wait.  */
>     while ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH)
> == 0x00);
>   }
> 
> 
> If PIT is not present all reads should return 0xff so this will always
> succeed, right? Linux kernel is using some sanity checks, if loop
> terminated too early it assumes calibration failure.

Well, yes the detection is bogus, I think the condition should check for
return 0x00, which means the timer is counting and can continue to wait
for it to finish.

   if ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH) == 0) {
     ret = 1;
     /* Wait.  */
     while ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH)
 == 0x00);
   }

Vitaly, could you please help to retest ?

Thanks,
Michael

>