Re: Elisp native profiler

[Eli Zaretskii]

> Date: Mon, 01 Oct 2012 07:54:51 -0700
> From: Paul Eggert <address@hidden>
> CC: address@hidden, address@hidden, address@hidden
> 
> > Will the signals caught during the period it was blocked
> > be reissued, and if so, how many times?
> 
> On modern POSIXish systems, the pending SIGPROF signal is delivered
> when the SIGPROF handler returns.  It's delivered just once.

That's what I thought.

> >From the user's point of view, if the sampling interval is too
> short, Emacs spends all its time profiling and refuses to do
> anything else.  I.e., it goes catatonic.

But on a modern multi-core machines, this shouldn't happen, I think.
Or should it?

Or how about setting SIGPROF to SIG_IGN while the handler runs?  Would
this make things better?

> We currently don't let the user set the sampling interval to be less
> than 1 ms, because our interface (perhaps unwisely) has millisecond
> resolution.  As far as we know, 1 ms works on all POSIXish platforms,
> and if so we don't have to worry about Emacs going catatonic, or about
> overrun counts, or the like.  If we changed the API to let users
> sample more often than 1 ms we would have to worry about this.

Well, you've just asked for such a change, AFAIR ;-)

> > Default value is just that: the default.  If there are bad
> > consequences possible when using very small sampling intervals,
> 
> Right now 1 ms is the default, and Stefan says that it works even on
> his slow platform, and we're guessing that means that it works
> everywhere of practical interest.

But if we do allow smaller values, I think we should display a
warning.