Re: [PATCH 0/2] printk: replace ringbuffer

[John Ogness]

On 2020-02-05, lijiang <lijiang@xxxxxxxxxx> wrote:
> Do you have any suggestions about the size of CONFIG_LOG_* and
> CONFIG_PRINTK_* options by default?

The new printk implementation consumes more than double the memory that
the current printk implementation requires. This is because dictionaries
and meta-data are now stored separately.

If the old defaults (LOG_BUF_SHIFT=17 LOG_CPU_MAX_BUF_SHIFT=12) were
chosen because they are maximally acceptable defaults, then the defaults
should be reduced by 1 so that the final size is "similar" to the
current implementation.

If instead the defaults are left as-is, a machine with less than 64 CPUs
will reserve 336KiB for printk information (128KiB text, 128KiB
dictionary, 80KiB meta-data).

It might also be desirable to reduce the dictionary size (maybe 1/4 the
size of text?). However, since the new printk implementation allows for
non-intrusive dictionaries, we might see their usage increase and start
to be as large as the messages themselves.

John Ogness