On Sat, Apr 09 2022 at 10:12, Kurt Kanzenbach wrote: > Introduce fast/NMI safe accessor to clock tai for tracing. The Linux kernel > tracing infrastructure has support for using different clocks to generate > timestamps for trace events. Especially in TSN networks it's useful to have TAI > as trace clock, because the application scheduling is done in accordance to the > network time, which is based on TAI. With a tai trace_clock in place, it becomes > very convenient to correlate network activity with Linux kernel application > traces. > > Use the same implementation as ktime_get_boot_fast_ns() does by reading the > monotonic time and adding the TAI offset. The same limitations as for the fast > boot implementation apply. The TAI offset may change at run time e.g., by > setting the time or using adjtimex() with an offset. However, these kind of > offset changes are rare events. Nevertheless, the user has to be aware and deal > with it in post processing. > > An alternative approach would be to use the same implementation as > ktime_get_real_fast_ns() does. However, this requires to add an additional u64 > member to the tk_read_base struct. This struct together with a seqcount is > designed to fit into a single cache line on 64 bit architectures. Adding a new > member would violate this constraint. > > Signed-off-by: Kurt Kanzenbach <kurt@xxxxxxxxxxxxx> Nice changelog! Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
