On 21/01/15 13:06, Steven Rostedt wrote:

On Wed, 21 Jan 2015 10:47:37 +0000
Daniel Thompson [off-list ref] wrote:

quoted

quoted

With this patchset, is it possible to call sched_clock() from within NMI
context? I ask because the generic sched_clock() code is not NMI safe

That's not good. Better not run function tracing, as that could trace
functions in NMI context (I depend on that it does), and it uses
sched_clock() as the default clock.

I think sched_clock is unsafe as in "may sometimes give the wrong value"
rather than "can lock up arbitrarily".  Thus the impact is unlikely to
be harmful enough to want to avoid tracing altogether.

It would require special care be taken when interpreting the timestamps
however. Also since update_sched_clock() is a notrace function its very
hard to figure out when timestamps are at risk.

Anyhow, the fix doesn't seem that hard. I can take a look.


Daniel.