On 15/02/2025 17:58, Guilherme G. Piccoli wrote: > TSC could be reset in deep ACPI sleep states, even with invariant TSC. > That's the reason we have sched_clock() save/restore functions, to deal > with this situation. But happens that such functions are guarded with a > check for the stability of sched_clock - if not considered stable, the > save/restore routines aren't executed. > > On top of that, we have a clear comment on native_sched_clock() saying > that *even* with TSC unstable, we continue using TSC for sched_clock due > to its speed. In other words, if we have a situation of TSC getting > detected as unstable, it marks the sched_clock as unstable as well, > so subsequent S3 sleep cycles could bring bogus sched_clock values due > to the lack of the save/restore mechanism, causing warnings like this: > > [22.954918] ------------[ cut here ]------------ > [22.954923] Delta way too big! 18446743750843854390 ts=18446744072977390405 before=322133536015 after=322133536015 write stamp=18446744072977390405 > [22.954923] If you just came from a suspend/resume, > [22.954923] please switch to the trace global clock: > [22.954923] echo global > /sys/kernel/tracing/trace_clock > [22.954923] or add trace_clock=global to the kernel command line > [22.954937] WARNING: CPU: 2 PID: 5728 at kernel/trace/ring_buffer.c:2890 rb_add_timestamp+0x193/0x1c0 > > Notice that the above was reproduced even with "trace_clock=global". > > The fix for that is to _always_ save/restore the sched_clock on suspend > cycle _if TSC is used_ as sched_clock - only if we fallback to jiffies > the sched_clock_stable() check becomes relevant to save/restore the > sched_clock. > Hi folks, I would like to ask if possible to add the following tag: Debugged-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxx> Cascardo helped me a lot on debugging this issue but I forgot to add it earlier, so nothing more fair than add it now! Thanks, Guilherme > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> > [...]
