Messages in this thread | | | Date | Thu, 18 Dec 2008 11:34:59 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v2] tracing/function-graph-tracer: prevent from hrtimer interrupt infinite loop |
| |
* Frederic Weisbecker <fweisbec@gmail.com> wrote:
> Impact: fix a system hang on slow systems > > While testing the function graph tracer on VirtualBox, I had a system hang > immediatly after enabling the tracer. > > If hrtimer is enabled on kernel, a slow system can spend too much time > during tracing the hrtimer_interrupt which will do eternal loops, > assuming it always have to retry its process because too much time > elapsed during its time update. Now we provide a feature which lurks at > the number of retries on hrtimer_interrupt. After 10 retries, the > function graph tracer will definetly stop its tracing.
hm, i dont really like this solution - it just works around the problem by 'speeding up' the system. If we have a _real_ slow system, there's no such way for us to speed it up.
Thomas, what do you think - would you expect this lockup to happen on really slow systems? If yes, is there a way we could avoid it from happening - by driving some sort of 'mandatory interval', that is doubled in size every time we detect such a bad hrtimer loop?
Ingo
| |