Re: [PATCH] xen/console: make console buffer size configurable

[Denis Mukhin <dmkhn@xxxxxxxxx>]

On Tuesday, February 18th, 2025 at 8:05 AM, Jan Beulich <jbeulich@xxxxxxxx> 
wrote:

>
>
> On 12.02.2025 23:31, dmkhn@xxxxxxxxx wrote:
>
> > --- a/xen/drivers/char/Kconfig
> > +++ b/xen/drivers/char/Kconfig
> > @@ -96,6 +96,18 @@ config SERIAL_TX_BUFSIZE
> >
> > Default value is 32768 (32KiB).
> >
> > +config CONRING_SIZE
> > + int "Console buffer size"
> > + default 32768
> > + range 16384 134217728
> > + help
> > + Select the boot console buffer size (in bytes).
>
>
> Why in bytes when ...
>
> > + Note, the value provided will be rounded down to the nearest power of 2.
>
>
> ... this rounding is done anyway? Why have people type in complicated numbers?
> A granularity of 1k would already be an improvement; yet better would be if
> this was a power-of-two value altogether.

My understanding that the semantics of new CONFIG_CONRING_SIZE build-time 
setting
should be consistent with existing boot-time conring_size= behavior (string 
value
converted to number of bytes).

I can update both to round up to 1k boundary.

I also agree that having power of 2s for both (e.g. similar to Linux'es 
CONFIG_LOG_BUF_SHIFT)
will be the simplest (implementation) and non-ambigous.
I had it done earlier:
  
https://lore.kernel.org/xen-devel/20241205-vuart-ns8250-v1-26-e9aa923127eb@xxxxxxxx/

Also, since there's a build-time configuration parameter along with the 
boot-time
configuration, perhaps it makes sense to retire boot-time setting in favor of
build-time setting?

>
> Jan