Re: [PATCH] Account for prologue spills in reg_pressure scheduling

[Sebastian Pop <sebpop@gmail.com>]

Ramana Radhakrishnan wrote:
> We already have sched-pressure --param=sched-pressure-algorithm=1 on
> by default in the AArch64 backend from September.
> https://gcc.gnu.org/ml/gcc-patches/2014-09/msg01663.html went in a few
> days back.
> 
>  So if this patch is on then we are looking at uplifts with
> sched-pressure-algorithm=2 patch and --param

Right: I ran "-O3" vs. "-O3 -fsched-pressure --param=sched-pressure-algorithm=1"
and the numbers are identical.

> sched-pressure-algorithm=2. To a large degree turning on algorithm #2
> is a benchmarking exercise and IMHO should happen along with the
> sched-pressure tweaks that you are currently doing.  I would suggest
> moving to the same algorithm as the ARM backend would be nice and if
> we can deal with any performance regressions that appear. However
> without seeing behaviour on some more benchmarks like SPEC2k(6) it
> would be unwise to switch this on by default . We can run this and let
> you know the results, though SPECFP2k6 takes quite a while - are all
> your patches to sched-pressure now done ?
> 
> >>
> >> These are great results, yay!
> >
> > +1.  Thanks for running these tests.  If you have time, it'd also be
> > interesting to try the same thing with --param=sched-pressure-algorithm=1
> > (which should be equivalent to not having the --param, but better safe
> > than sorry).  Is algorithm 1 or algorithm 2 better for aarch64?

When testing Maxim's patch + --param=sched-pressure-algorithm=1
I see more perf degradations than speedups.

> Sebastian's results indicate algorithm #2 + Maxim's patches are better
> but we probably need some more benchmarking.

Overall algorithm #2 produces better results than algorithm #1.  Maxim's patch
is nicely improving the perf of algorithm #2.

Thanks,
Sebastian