Re: [PATCH v2] i386: Make pmtimer tsc calibration not take 51 seconds to fail

[Robbie Harwood]

Paul Menzel <pmenzel@molgen.mpg.de> writes:

> Am 29.05.20 um 12:08 schrieb Javier Martinez Canillas:
>
>> +/*
>> + * Define GRUB_PMTIMER_IGNORE_BAD_READS if you're trying to test a timer 
>> that's
>> + * present but doesn't keep time well.
>> + */
>> +// #define GRUB_PMTIMER_IGNORE_BAD_READS
>
> So GRUB needs to be rebuild for both cases? Could it be configured at
> runtime with a config option, or is the TSC calibration happening too
> early?

Not an author, but my understanding is that that's a configuration
intended for testing only.  e.g., from the commit message:

> This outcome was tested using grub compiled with
> GRUB_PMTIMER_IGNORE_BAD_READS defined (so as not to trip the bad read
> test) using qemu+kvm with UEFI (OVMF) firmware, and these options:
> -machine pc-q35-2.10 -cpu Broadwell-noTSX

which I take to mean that Peter did not have a machine with a timer that
misbehaved but didn't return 0 or 0xffffffff, yet wanted a way to test
that codepath.  This wouldn't be a configuration that I can imagine
anyone wanting to ship, so I don't really see value in having it
available at runtime.  Hope that helps.

Be well,
--Robbie

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