On Wed, Feb 13, 2019 at 9:19 PM Petr Mladek <pmla...@suse.com> wrote: > > On Wed 2019-02-13 14:19:01, xiang xiao wrote: > > On Wed, Feb 13, 2019 at 3:46 AM Steven Rostedt <rost...@goodmis.org> wrote: > > > > > > On Wed, 13 Feb 2019 02:11:05 +0800 > > > Xiang Xiao <xiaoxiang781...@gmail.com> wrote: > > > > > > > Because log may already add the timestamp sometime > > > > > > Can you be a bit more detailed on this. When and where does this > > > happen? > > > > Here is my case: > > 1.A small MCU(Cortex M4) in SoC run RTOS > > 2.RTOS append timestamp to log for the accurate timing > > 3.RTOS send log to Linux kernel when buffer exceed the threshold > > What do you exactly mean by the threshold, please?
The current algorithm is: 1.the free space is less than 25% or 2.the idle time is large than 100ms > Does it mean > that you use the kernel buffer when there are too many messages > and they do not fit into the MCU local buffer? The buffering just happen in MCU side, kernel don't do any buffering except waiting for '\n' before printk. > > How exactly the kernel gets the messages, please? > Via a kernel driver or from userspace (via /dev/kmsg)? > It's a kernel rpmsg driver: https://github.com/thesofproject/linux/pull/177/commits/a0b7009fede5552dc98733f2996a8140bff62455 > > > 4.Kernel call printk to dump the received buffer > > So I want that printk skip the timestamp here. > > If the messages are printed by a kernel driver then > a better solution would be to create a printk() API > where you could pass the time stamp as a parameter. Yes, this is a better approach and could fix all issues you list below. > > The aim is to store the precise time stamp in ts_nsec, struct > printk_log. Then it will get handled correctly by any > output, e.g. consoles, syslog, /dev/kmsg. > > > There are several problems with your approach: > > 1. The time stamp is still duplicated in the output via /dev/kmsg, > see msg_print_ext_header(). We could not change this > because the time stamp is part of the format. > Any change could break userspace (systemd). > > > 2. The time stamp stays part of the message: > > + It might have different format than the normal > time stamp. Therefore it might be hard to filter > > + dmesg might be unable to parse it and show in > the other formats. > > + Kernel-5.1 will allow to print information > about the caller. It is supposed to be between > the time stamp and the message text, see > > http://lkml.kernel.org/r/93f19e57-5051-c67d-9af4-b17624062...@i-love.sakura.ne.jp > > > Best Regards, > Petr
