On 05.03.2025 02:12, dm...@proton.me wrote:
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -425,10 +425,13 @@ The following are examples of correct specifications:
> ### conring_size
> > `= <size>`
>
> -> Default: `conring_size=16k`
> +> Default: `conring_size=32k`
>
> Specify the size of the console ring buffer.
>
> +The console ring buffer size can be selected at build time via
> +CONFIG_CONRING_SHIFT.
And hence, if a value other than 32 is used there, the default above is
going to be wrong. IOW it is only the compile time default which is 32k.
The run-time default (which is what matters in Default: above) is itself
configurable, and hence wants documenting that way.
> --- a/xen/drivers/char/Kconfig
> +++ b/xen/drivers/char/Kconfig
> @@ -96,6 +96,33 @@ config SERIAL_TX_BUFSIZE
>
> Default value is 32768 (32KiB).
>
> +config CONRING_SHIFT
> + int "Console buffer size (power of 2)"
Would you mind adding the word "ring" here?
> + range 14 27
> + default 15
> + help
> + Select the boot console buffer size as a power of 2.
> + Run-time console buffer size is the same as the boot console size,
> + unless overridden via 'conring_size=' boot parameter.
> +
> + Default value is 15 (32KiB).
> +
> + Examples:
> + 27 => 128 MiB
> + 26 => 64 MiB
> + 25 => 32 MiB
> + 24 => 16 MiB
> + 23 => 8 MiB
> + 22 => 4 MiB
> + 21 => 2 MiB
> + 20 => 1 MiB
> + 19 => 512 KiB
> + 18 => 256 KiB
> + 17 => 128 KiB
> + 16 => 64 KiB
> + 15 => 32 KiB
> + 14 => 16 KiB
I don't think an exhaustive list is necessary here. This way it's not really
a set of examples, but an enumeration of all possible values.
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -101,12 +101,12 @@ static int cf_check parse_console_timestamps(const char
> *s);
> custom_runtime_param("console_timestamps", parse_console_timestamps,
> con_timestamp_mode_upd);
>
> -/* conring_size: allows a large console ring than default (16kB). */
> +/* conring_size: override build-time CONFIG_CONRING_SHIFT setting. */
> static uint32_t __initdata opt_conring_size;
> size_param("conring_size", opt_conring_size);
>
> -#define _CONRING_SIZE 16384
> -#define CONRING_IDX_MASK(i) ((i)&(conring_size-1))
> +#define _CONRING_SIZE (1UL << CONFIG_CONRING_SHIFT)
Imo this ought to be 1U only, seeing ...
> +#define CONRING_IDX_MASK(i) ((i) & (conring_size - 1))
> static char __initdata _conring[_CONRING_SIZE];
> static char *__read_mostly conring = _conring;
> static uint32_t __read_mostly conring_size = _CONRING_SIZE;
... this use of the constant.
Jan
