On 2016.09.23 at 14:19 +0000, Wilco Dijkstra wrote:
> Richard Biener wrote:
> >On Fri, Sep 23, 2016 at 3:02 PM, Markus Trippelsdorf
> ><mar...@trippelsdorf.de> wrote:
> > > And tramp3d only uses ten partitions (lto-min-partition=10000).
> > > With lto-min-partition=50000 (current patch) this decrease to only two
> > > partitions. As a result we loose the possible speedup on many core
> > > machines (-flto=n).
>
> Only if the size is close to the lto-min-partition. For larger applications
> there is
> little difference.
>
> > > E.g. on my 4-core machine I get the following tramp3d compile times with
> > > -flto=4:
> > >
> > > lto-min-partition=50000: 20.146 total
> > > lto-min-partition=10000: 16.299 total
> > > lto-min-partition=1000 : 16.093 total
> > >
> > > So 50000 looks too big to me.
>
> That's only 16 seconds? Seems like it's small so ideally it should have
> used a single partition...
What I wanted to point out is that you of course loose the speedup you'll
get from parallel running backends with only a single partition.
% time g++ -w -Ofast tramp3d-v4.cpp
g++ -w -Ofast tramp3d-v4.cpp 25.61s user 0.31s system 99% cpu 25.944 total
% time g++ -flto=4 -w -Ofast tramp3d-v4.cpp
g++ -flto=4 -w -Ofast tramp3d-v4.cpp 28.15s user 1.02s system 181% cpu 16.075
total
% time g++ --param=lto-partitions=1 -flto=4 -w -Ofast tramp3d-v4.cpp
g++ --param=lto-partitions=1 -flto=4 -w -Ofast tramp3d-v4.cpp 26.98s user
0.57s system 99% cpu 27.629 total
--
Markus
