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

[Julien Grall <julien@xxxxxxx>]

On 05/01/2023 09:59, Ayan Kumar Halder wrote:
> Hi Julien,
Hi,

> I have a clarification.
>
> On 05/01/2023 09:26, Julien Grall wrote:
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> >
> > 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.
> For RTOS (Zephyr and FreeRTOS), it should be possible for guests to have 
> memory less than 1 MB, isn't it ?
Yes. So does XTF. But most of the users are likely going allocate at 
least 1MB (or even 2MB to reduce the TLB pressure).
So it would be better to print the value in a way that is more 
meaningful for the majority of the users.
> > So I would consider to check the size is 1MB-aligned and then print the
I will retract my suggestion to check the size. There are technically no 
restriction to run a guest with a size not aligned to 1MB. Although, it 
would still seem strange.
Cheers,

--
Julien Grall