Re: [PATCH for-xen-4.5] console: increase initial conring size

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 02/12/14 14:57, Daniel Kiper wrote:
> In general initial conring size is sufficient. However, if log
> level is increased on platforms which have e.g. huge number
> of memory regions (I have an IBM System x3550 M2 with 8 GiB RAM
> which has more than 200 entries in EFI memory map) then some
> of earlier messages in console ring are overwritten. It means
> that in case of issues deeper analysis can be hindered. Sadly
> conring_size argument does not help because new console buffer
> is allocated late on heap. It means that it is not possible to
> allocate larger ring earlier. So, in this situation initial
> conring size should be increased. My experiments showed that
> even on not so big machines more than 26 KiB of free space are
> needed for initial messages. In theory we could increase conring
> size buffer to 32 KiB. However, I think that this value could be
> too small for huge machines with large number of ACPI tables and
> EFI memory regions. Hence, this patch increases initial conring
> size to 64 KiB.
>
> Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>

For what it is worth, XenServer has been been using a 64k default
console size for a very long time now.

However, a change line this must include a change to
docs/misc/xen-command-line.markdown

~Andrew

> ---
>  xen/drivers/char/console.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> index 2f03259..429d296 100644
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -67,7 +67,7 @@ custom_param("console_timestamps", parse_console_timestamps);
>  static uint32_t __initdata opt_conring_size;
>  size_param("conring_size", opt_conring_size);
>  
> -#define _CONRING_SIZE 16384
> +#define _CONRING_SIZE 65536
>  #define CONRING_IDX_MASK(i) ((i)&(conring_size-1))
>  static char __initdata _conring[_CONRING_SIZE];
>  static char *__read_mostly conring = _conring;