Re: [PATCH v2 5/8] tools/hvmloader: Retrieve (x2)APIC IDs from the APs themselves

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, May 24, 2024 at 04:16:01PM +0100, Alejandro Vallejo wrote:
> On 23/05/2024 17:13, Roger Pau Monné wrote:
> > On Wed, May 08, 2024 at 01:39:24PM +0100, Alejandro Vallejo wrote:
> >> @@ -86,10 +113,11 @@ static void boot_cpu(unsigned int cpu)
> >>          BUG();
> >>  
> >>      /*
> >> -     * Wait for the secondary processor to complete initialisation.
> >> +     * Wait for the secondary processor to complete initialisation,
> >> +     * which is signaled by its x2APIC ID being writted to the LUT.
> >>       * Do not touch shared resources meanwhile.
> >>       */
> >> -    while ( !ap_callin )
> >> +    while ( !ACCESS_ONCE(CPU_TO_X2APICID[cpu]) )
> >>          cpu_relax();
> > 
> > As a further improvement, we could launch all APs in pararell, and use
> > a for loop to wait until all positions of the CPU_TO_X2APICID array
> > are set.
> 
> I thought about it, but then we'd need locking for the prints as well,
> or refactor things so only the BSP prints on success.

Hm, I see, yes, we would likely need to refactor the printing a bit so
each AP only prints one line, and then add locking around the calls in
`cpu_setup()`.

> The time taken is truly negligible, so I reckon it's better left for
> another patch.

Oh, indeed, sorry if I made it look it should be part of this patch,
that wasn't my intention.  Just something that might be worth looking
into doing in the future.

Thanks, Roger.