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

> [Adding ARM maintainers to CC]
> On Oct 21, 2014, at 9:44 AM, Sebastian Pop <> wrote:
> > Hi Maxim,
> >
> > Maxim Kuvyrkov wrote:
> >> Thanks, benchmarking results are welcome!  AArch64 doesn't use
> >> reg_pressure scheduling by default.  Use "-fsched-pressure
> >> --param=sched-pressure-algorithm=2" to enable same thing as on ARM.
> >> I would imagine C++ and Fortran floating-point code to be most
> >
> > On aarch64 I only see perf improvements with your patch: no perf
> > degradations on all the tests that I have run.
> >
> > base0: r216447, -O3
> > base1: r216447, -O3 -fsched-pressure
> > --param=sched-pressure-algorithm=2
> > patch: r216447 + your patch, -O3 -fsched-pressure
> > --param=sched-pressure-algorithm=2
> >
> > patch vs. base1 is only an improvement.
> >
> > base1 vs. base0 has a few good improvements, and some small
> > degradations: your patch improves the perf for one of the degradations
> > to the point it is better now with -fsched-pressure
> algorithm=2 than at -O3.
> >
> > Could we turn on "-fsched-pressure --param=sched-pressure-algorithm=2"
> > by default for aarch64?
> These are great results, yay!  Sebastian, what benchmarks did you run?
> We need to see improvements on spec2k / spec2k6 to enable
> scheduling on AArch64 by default.  The current understanding is that
> has enough registers to not benefit from pressure-aware scheduling.  On
> other hand, one could argue that cores with more complex pipelines (e.g.,
> A57) might not benefit from pipeline-oriented scheduling either, and,
> therefore, scheduling for register pressure can provide a better win.

Cores with complex pipelines might benefit less from such scheduling, but if
x86-64, which is as complex as it gets, generally benefitted from other
scheduling algorithms at least, I'd wager that A57 could experience some
boost as well.


Evandro Menezes                              Austin, TX

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