On Fri, 2012-12-07 at 11:07 +0900, Hiraku Toyooka wrote:
> Hi, Steven,
>
> (2012/11/30 23:17), Steven Rostedt wrote:
> [snip]
> >
> > Actually, I would have:
> >
> > status\input | 0 | 1 | else |
> > --------------+------------+------------+------------+
> > not allocated |(do nothing)| alloc+swap | EINVAL |
> > --------------+------------+------------+------------+
> > allocated | free | swap | clear |
> > --------------+------------+------------+------------+
> >
> > Perhaps we don't need to do the clear on swap, just let the trace
> > continue where it left off? But in case we should swap...
> >
>
> I think we don't need the clear on swap too.
> I'll update my patches like this table.
>
> > There's a fast way to clear the tracer. Look at what the wakeup tracer
> > does. We can make that generic. If you want, I can write that code up
> > too. Hmm, maybe I'll do that, as it will speed things up for
> > everyone :-)
> >
>
> (I looked over the wakeup tracer, but I couldn't find that code...)
Heh, sorry, you needed to look at the "update_max_tr()" in
kernel/trace/trace.c. Where we update the time_start value. Then the
output skips all timestamps before that start. This is much more
efficient than a 'reset', as we don't need to sync or anything. Just
record the timestamp of where we want to consider the buffer started,
and ignore any event before that.
> I think that seq_read() calls s_stop() even if s_start() failed.
>
> seq_read()@fs/seq_file.c:
>
> p = m->op->start(m, &pos);
> while (1) {
> err = PTR_ERR(p);
> if (!p || IS_ERR(p))
> break;
> ...
> }
> m->op->stop(m, p);
>
> So, I think we need the check in s_stop(), don't we?
Crap, you're right. Hmm, why was I thinking that it didn't. I better go
and review some of my recent code to make sure that I didn't have that
wrong assumption.
-- Steve
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