On Wed, Nov 03, 2010 at 04:10:30PM -0400, Adam Jackson wrote:
On Wed, 2010-11-03 at 19:58 +0100, Jakub Jelinek wrote:
> On Wed, Nov 03, 2010 at 02:48:12PM -0400, Owen Taylor wrote:
> > Basically summarizes the situation, and as far as I know nothing has
> > changed ... with default compilation options, getting callgraph
> > profiling on x86_64 really requires a DWARF unwinder in the kernel.
> > Which seems unlikely to happen.
>
> But that's the right thing to do.
Sure, but so is a kernel debugger, and it's taken us over ten years to
get one. I'm pretty okay with doing something wrong now if it gets me
something usable for long enough to get something right later. I'll
take 4% across the board if it helps me find the 20% that matters.
Most of the time you don't find the 20% improvements with profilers though,
so all we end up with is just slowing everything by 4%. Definitely a bad
idea, now that per core performance doesn't increase very much and most
programs aren't parallelized at all or just very badly.
Jakub