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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.02.2025 21:52, Denis Mukhin wrote:
> 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/

I'd prefer the power-of-2 approach, yet I could live with the Kb-based one as
was suggested by Roger.

> 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?

Why would that be? Build-time settings can only ever be defaults. We don't
know what people need in their configurations.

Jan