Re: [PATCH gnumach] lapic timer: Calibrate based on 10 PIT sleeps for 10ms

[Damien Zammit]

On 26/2/23 20:20, Samuel Thibault wrote:
> Samuel Thibault, le dim. 26 févr. 2023 10:03:28 +0100, a ecrit:
>> Damien Zammit, le dim. 26 févr. 2023 03:34:59 +0000, a ecrit:
>>> On 26/2/23 12:31, Damien Zammit wrote:
>>>> NB: This relies on a fix for QEMU as one-shot PIT mode
>>>> is currently broken in qemu.
>>>
>>> Here is the corresponding qemu patch:
>>>
>>> https://lists.nongnu.org/archive/html/qemu-devel/2023-02/msg07549.html
>>
>> I'm afraid this means we should refrain from using this mode.
>>
>> Because this mode being buggy in qemu means that OSes don't usually use
>> it, which means that virtualization tools most probably don't notice
>> their bugs in this mode.
>
> (meaning: it'll be a perpetual burden, and people will criticize
> the Hurd « it doesn't even run under <whatever yet other bugged
> virtualization tool> »)

I don't know how else to calibrate the local apic timer. How should we do it?
Intel cpus have varying bus clocks and they are all slightly different.
The PIT provides a constant clock speed based on a crystal oscillator so
is the simplest choice to calibrate any other timer.

Isn't that the beauty of free software, that bugs can be fixed?
The PIT code works on native hardware and I have provided a patch to fix qemu.

Damien