Em Wed, Nov 27, 2013 at 11:51:25PM +0900, Namhyung Kim escreveu:
> 2013-11-27 (수), 11:41 -0300, Arnaldo Carvalho de Melo:
> > Em Wed, Nov 27, 2013 at 11:17:43PM +0900, Namhyung Kim escreveu:
> > > 2013-11-27 (수), 10:44 -0300, Arnaldo Carvalho de Melo:
> > > > Same signature, 32-bit, 64-bit userland, so whoever wrote timechart,
> > > > Arjan, I
> > > > think, made no mistakes at using the kernel exported interface,
> > > > choosing the
> > > > most efficient way to extract the data, casting to a struct.
> > > > Yeah, using the interface that searches for a field name to get the
> > > > offset and
> > > > then add it to a pointer to then cast to the type will allow maximum
> > > > flexibility,
> > > > but is not really efficient.
> > > > Doing that for something that is not performance critical (probably) as
> > > > timechart probably is not a problem, but so is not a problem using the
> > > > patch
> > > > that does the cast after finding the offset of the first non-common
> > > > field.
> > > I'm not sure how it affects the performance really.
> > Hey, everytime we need to get the value of a field when processing each
> > tracepoint sample we need to do it via:
> > struct format_field *pevent_find_field(struct event_format *event, const
> > char *name)
> > {
> > struct format_field *format;
> >
> > for (format = event->format.fields; format; format = format->next) {
> > if (strcmp(format->name, name) == 0)
> > break;
> > }
> >
> > return format;
> > }
> >
> > I don't think this is optimal, no.
> >
> > But yeah, for things that don't have performance needs, don't process that
> > many
> > samples and hey, machines are fast and cheap these days ;-)
>
> Right. What I wanted to say actually was like s/how/how much/. :)
We would have to use perf for that 8-)
Its just that doing a string search on a doubly linked list for each
field on each sample doesn't _look_ optimal to me, so I didn't bother
using a profiler for that :-)
Anyway, lets move on, will apply the patch after lunch and send Ingo's
way.
- Arnaldo
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