Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

[Masami Hiramatsu]

Steven Rostedt wrote:
> On Mon, 23 Feb 2009, Ingo Molnar wrote:
> 
>> * Steven Rostedt <rostedt@goodmis.org> wrote:
>>
>>>> Which would send a delayed work to wake up?
>>> No, I was thinking that trace_delay_wake_up() would be called 
>>> by these dangerous call sites. Then a per_cpu flag could be 
>>> set. We could have a trace point in the scheduler code that is 
>>> outside holding a runqueue lock, and this trace point would 
>>> call a trace function that will clear the per cpu flag, and 
>>> then call trace_wake_up().
>> No, that's very roundabout and ugly. If we putting a tracepoint 
>> there we might as well put real scheduler code there that looks 
>> for such a flag. But i'm not convinced we need a flag ...
> 
> Just a suggestion. I was trying to keep the tracer from being an overhead. 
> But what else would you suggest? Just having the scheduler call 
> trace_wakeup?

Actually, Systemtap(LTTng too?) also has same problem. Currently,
we're using a periodical timer to wake the reader process up.
I assume if we can put a tracepoint at the beginning of schedule(),
we can share it.

Thank you,


> 
> -- Steve
> 
> --
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-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com