Re: [ANNOUNCE] New utility: 'trace'

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(2010/11/18 0:43), Peter Zijlstra wrote:
> On Wed, 2010-11-17 at 10:10 -0500, Steven Rostedt wrote:
>>
>> Right, the problem with filtering is what do we want to filter, and what
>> about copying?
>>
>> Currently, we copy the data into the buffer and then filter on that
>> data. We could also easily filter on the parameters of the tracepoint,
>> but sometimes those parameters do not match the final output (as the
>> case with sched_switch). Do we copy the data into a separate "per cpu"
>> temp buffer, and figure out the filter then? And if the filter is fine,
>> then copy into the buffer. This obviously is slow, due to the multiple
>> copies. We could do this only if the filtering is enabled.
> 
> Right, so what is the primary purpose of this filtering stuff? As it
> stands it makes stuff terribly slow, so you add overhead but the win
> (presumably) is less data output, is that a sane trade-off?
> 
> Most people I've heard -- both at LinuxCon.JP and LPC -- are asking for
> lower overhead tracing (while at the same time demanding more features).

I've also heard a dynamic filtering (or kicking buffer snapshot) request
in LinuxCon.JP. I think filtering is not only for filtering-out purpose,
but also useful for hooking event to take some action. :)

Thank you,


-- 
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com