On 8/5/20 10:04 AM, Petr Mladek wrote: > On Wed 2020-07-29 08:22:36, Prarit Bhargava wrote: >> Chunyan Zhang <zhang.lyra@xxxxxxxxx> wrote: >>> From: Prarit Bhargava <prarit@xxxxxxxxxx> >>> >>> printk.time=1/CONFIG_PRINTK_TIME=1 adds a unmodified local hardware clock >>> timestamp to printk messages. The local hardware clock loses time each >>> day making it difficult to determine exactly when an issue has occurred in >>> the kernel log, and making it difficult to determine how kernel and >>> hardware issues relate to each other in real time. >>> >>> Make printk output different timestamps by adding options for no >>> timestamp, the local hardware clock, the monotonic clock, the boottime >>> clock, and the real clock. Allow a user to pick one of the clocks by >>> using the printk.time kernel parameter. Output the type of clock in >>> /sys/module/printk/parameters/time so userspace programs can interpret the >>> timestamp. >>> >> ISTR the reason that this was dropped was because of the a problem with >> the way systemd read the kernel's timestamps. It got the attention of >> Linus, and it was then pulled from the tree. >> >> I need to go back and review the entire thread as it's been several years >> since we had the discussion although ISTR someone mentioning that doing two >> timestamps would not be a problem for systemd. > > I guess that you talk about this thread > https://lore.kernel.org/lkml/CA+55aFwUfA__6MgMgjENnx+_RYY2ZOOLiSx2ea1AvYhSZN+78A@xxxxxxxxxxxxxx/ > >> For example, >> >> [48551.015086] >> >> would be >> >> [48551.015086] m[xxxx.xxxx] >> >> for the monotonic clock timestamp, and >> >> [48551.015086] b[xxxx.xxxx] >> >> for the boottime clock, etc. > > This approach has several drawbacks: > > + Too long prefix might make it hard to see the real messages > because of shrunken/wrapped lines. > > + Too long lines are problem with slow consoles. > > + More space will be necessary to store all the time stamps. > > + Userspace tools would need/want to parse the format. We would > need to maintain it forever. > > > Linus had an interesting idea to print all timestamps regularly. > The frequency might be configurable. It might print, for example, > the following line every 10 minutes or once a day: > > [48551.015086] System alive: b[xxxx.xxxx] m[xxxx.xxxx] > > It might be useful in general to see when the system was still alive > before it froze. > > Would it be enough to sort messages printed with different clock > sources? Hey Petr, After reviewing the thread (it has been three years after all), I have asked Orson and Lyra to look at the suggested changes by tglx and Linus and submit those instead of "this" patch. I should have updated this thread with that info. Sorry 'bout that. P.
