On 13/12/2017 at 09:33:23 +0100, Arnd Bergmann wrote: > On Wed, Dec 13, 2017 at 6:47 AM, Baolin Wang <baolin.wang@xxxxxxxxxx> wrote: > > > >>> diff --git a/include/trace/events/rtc.h b/include/trace/events/rtc.h > >>> new file mode 100644 > >>> index 0000000..b5a4add > >>> --- /dev/null > >>> +++ b/include/trace/events/rtc.h > >>> + > >> > >> Also, I'm a bit concerned about having a struct rtc_time here. I think > >> its goal is mainly to have a nice representation on the time but maybe > > > > Yes. > > > >> the best would be to make printk able to pretty print the time (some > >> patches were proposed). > > > > If I understood your point correctly, you did not like the format of > > TP_printk() here, right? So how about if I remove the 'struct > > rtc_time' and just pass one 'ktime_t' parameter? But it will be not > > readable for user to trace the RTC time/alarm. > > > >> > >> How bad would that be to change it later? I didn't follow the whole > >> tracepoint ABI issue closely. > > There is no general rule here other than "if it breaks for existing > users, we have to fix it". Anyone who uses the tracepoints correctly > would end up showing zero-date if we change all the fields, but > it should not crash here. > > Printing a time64_t instead of rtc_time may be better here, as it's > cheaper to convert rtc_time to time64_t that vice versa. User space > looking at the trace data can then do the conversion back to struct tm > for printing in a C program or using /bin/date from a shell > script, but I agree it's an extra step. > > It's also possible that we don't care about the overhead of doing > a time64_to_tm() or rtc_time64_to_tm() in the trace function, as long > as that only needs to be done if the tracepoint is active. I find trace > points a bit confusing, so I don't know if that is the case or not when > the tracepoint is compiled into the kernel but disabled at run time. > Sorry, I was not clear and I never actually used tracepoints. My point was that the printk format is nice and can probably be kept as is. But I would like tracepoint to take a time64_t instead of an rtc_time even if that means having a conversion before calling the tracepoint and converting back to display the date/time. Also, I think we could try having only the time64_t in the ring buffer. Maybe I'm wrong but I think tools reading that buffer can do the conversion themselves. Maybe I don't understand correctly how tracepoints work and this doesn't make sense, tell me. The printk patches I was referring to are: https://marc.info/?l=linux-rtc&m=149693060517054&w=2 But they don't provide a way to pretty print a time64_t yet (it was just suggested by Arnd). -- Alexandre Belloni, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com
