On Thu, May 3, 2012 at 7:21 AM, Arun KS [off-list ref] wrote:

Hi Chetan,

On Thu, May 3, 2012 at 3:35 PM, Chetan Nanda [off-list ref]
wrote:

quoted

Hi,

We are working on ARM based SOC.
Currently we are implementing a efficient tracing mechanism to logs

messages

quoted

from a dedicated MCU.

For this, we share a circular buffer between ARM and MCU and messages

stored

quoted

in the buffer will be put into kernel ring-buffer and then output via

dmesg

quoted

call.
Strangely wringing a single log message in the kernel ring-buffer cost
around 6-8ms.

Consider this situvation, if your do a printk message of 100
characters at a baud rate of 115200 bps on your UART console.
Now 1 bit it will take 8.68 us(ie.. 1/115200).

So 100 character ie.. 800 bits(exculuding parity, stop bits and all
other over heads) will take 8.68 us * 800 = 6.94 ms.

How are you writing to the kernel log buffer?
Are you using UART as console? If yes what is your baud rate?

If possible give more details about your design.

I think Arun's assumptions are valid here. I am not aware of how the

kernel ring buffer is used, but I would think it is better to have the logs
printed out from a user space application. That way you are not blocking
the kernel to spend time printing each message that gets put into the
buffer. Does that make sense?

Thanks,

Arun

quoted

Please help to confirm this, or we are doing something wrong.

Thanks,
Chetan Nanda

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