Re: RFC[1/2] Common logging infrastructure and API

Saucedo Tejada, Genaro <genaro.saucedo.tejada@...>

On Tue, 2016-03-01 at 16:15 +0000, Chereau, Fabien wrote:

-----Original Message-----
From: Tomasz Bursztyka [mailto:tomasz.bursztyka(a)]
Sent: Tuesday, March 1, 2016 16:55
To: devel(a)
Subject: [devel] Re: Re: Re: Re: Re: RFC[1/2] Common logging
and API

Hi Luiz,

- Another feature which is critical for Curie, is the support
of multi-core
logging. One core is the master outputting the log on the
log_backend while
other slaves cores send their logs to the master using an IPC
Each log message carries the information from which core it
originates, +  a
unified timestamp.
-1, this depends on the hardware architecture besides one can
write a
driver to just proxy the logs.
I don't see anything we could do about that in this logging API.
If there is something to be done, let's see it in another patch.
Indeed, my point was just to make sure at API level that such custom
implementations are pluggable.
I understand, for this first effort the goal is to unify calls under a
single API that can be later provided by different implementations. I
don't foresee conflicts between initial proposal and Fabien's insights.

- Finally, another important feature we implemented is the
buffering of
incoming logs in a circular buffer in RAM (on both master and
slave). This
allow very short log time to avoid delaying the caller of the log
function. The
logs are finally output on the log backend in a low priority task,
which reads
from the circular buffer. In case there are too many incoming logs,
some logs
are lost instead of blocking the program execution.
Provided the message order is keep that is probably ok, but if we
add the timestamp support then it needs to be before it enters
buffers. Anyway we may add timestamp support for net_buf at some
point. Btw, having it as a task probably limits this to
only doesn't it?
Nanokernel could get it, it would run in low prio fiber and that's

Imo, let's not bother fixing this right now in this API. This goes
(as I said, instead of having printk/printf we could have a new
sys_log() functions that could act
as a log buffering proxy, fully optional etc...)


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