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

[Andrei Borzenkov]

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?
> 


  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.