Re: [PATCH v2] xen/arm: Add 0x prefix when printing memory size in construct_domU

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 04/01/2023 23:47, Stefano Stabellini wrote:
> On Tue, 3 Jan 2023, Michal Orzel wrote:
> > Printing memory size in hex without 0x prefix can be misleading, so
> > add it. Also, take the opportunity to adhere to 80 chars line length
> > limit by moving the printk arguments to the next line.
> >
> > Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> > ---
> > Changes in v2:
> >   - was: "Print memory size in decimal in construct_domU"
> >   - stick to hex but add a 0x prefix
> >   - adhere to 80 chars line length limit
> Honestly I prefer decimal but also hex is fine. 
decimal is perfect for very small values, but as we print the amount in 
KB it will become a big mess. Here some examples (decimal first, then 
hexadecimal):
  512MB: 524288 vs 0x80000
  555MB: 568320 vs 0x8ac00
  1GB: 1048576 vs 0x100000
  512GB: 536870912 vs 0x20000000
  1TB: 1073741824 vs 0x40000000

For power of two values, you might be able to find your way with 
decimal. It is more difficult for non power of two unless you have a 
calculator in hand.
The other option I suggested in v1 is to print the amount in KB/GB/MB. 
Would that be better?
That said, to be honest, I am not entirely sure why we are actually 
printing in KB. It would seems strange that someone would create a guest 
with memory not aligned to 1MB.
So I would consider to check the size is 1MB-aligned and then print the 
value in KB. This will remove one order of magnitude and make the value 
more readable in decimal.
Cheers,

--
Julien Grall