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Re: [lmi] Compiling takes longer with gcc-4.9.2
From: |
Greg Chicares |
Subject: |
Re: [lmi] Compiling takes longer with gcc-4.9.2 |
Date: |
Mon, 18 Jan 2016 02:44:32 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.3.0 |
On 2016-01-17 18:36, Vadim Zeitlin wrote:
> On Sun, 17 Jan 2016 17:51:45 +0000 Greg Chicares <address@hidden> wrote:
>
> GC> On 2015-12-22 00:28, Greg Chicares wrote:
> GC> > My local tree contains makefile changes to use MinGW-w64 gcc-4.9.2,
> GC> > with '-std=c++11', some new warning flags, and various other
> GC> > adjustments.
> GC>
> GC> I'm almost ready to commit those changes. First, however, I tried them
> GC> out on different hardware, and found a PCH surprise. Timings quoted
> GC> from the 2015-12-22 original used old hardware; new timings reported
> GC> today use new hardware unless explicitly indicated otherwise.
> GC>
> GC> old: 2 x E5520, 3 Gbps sata ii, wd black WD2003FZEX, debian-7.7
> GC> new: 2 x #5-2530 v3, 6 Gpbs sata iii, samsung 850 pro 1TB, debian-7.9
> ^^^^^^^
> This is probably E5-2630.
Yes. I used to be able to touch-type numbers. Letters, too.
> GC> I expect the new hardware to perform uniformly better than the old.
>
> I would obviously expect it as well... Something seems to be really wrong
> here, especially with
>
> GC> > make --jobs=8 -f install_wx.make > ../log 2>&1
> GC> > 2662.23s user 1594.59s system 475% cpu 14:55.38 total
> GC>
> GC> make --jobs=8 -f install_wx.make > ../log 2>&1
> GC> 2727.15s user 6098.59s system 214% cpu 1:08:39.33 total
>
> this, of course. It takes twice less of the CPU time yet 4 times the wall
> time? I just can't fathom this.
I was using
--host=i686-pc-mingw32
where this
--host=i686-w64-mingw32
is wanted. I'll have to retest now. I wonder why that even worked, or
seemed to.
> GC> The bottleneck might even be the preprocessor.
>
> So the IO layer then? It looks plausible but this would just mean that KVM
> doesn't do its job well.
'virtio' drivers are provided for most popular OS's. But there is none
for msw-xp; or, properly speaking, IIRC, one exists, but it does nothing,
and its author recommends against using it.
> I know you don't want to use it but I'm really
> curious to know how faster would the compilation inside the same VM be
> inside VMware.
Is installing it as simple as 'apt-get [whatever]'? Would installing it
pull in lots of changes I don't want? Is it provided by debian, in the
"free" repository--or does it require "nonfree", or, worse, an external
repository? I could consider this now that I have two machines that can
run VMs--it's not a catastrophe if I destabilize the backup.
> GC> New hardware makes a small difference for gcc-4.9.2, though it seemed
> GC> to make no difference for gcc-3.4.5 .
>
> I'd like to see your numbers for cross-compiling. Normally they should be
> significantly better than mine (and so an order of magnitude better than
> what you have now), if this is not the case neither I'd seriously start
> suspecting some hardware problem in the new machine.
Cross-compiling from GNU/Linux: all in due time. First I need to get
the i686-pc-cygwin + i686-w64-mingw32 combination working, so that it
can be tested in the office.
Re: [lmi] Compiling takes longer with gcc-4.9.2, Greg Chicares, 2016/01/18
[lmi] KVM performance [Was: Compiling takes longer with gcc-4.9.2], Greg Chicares, 2016/01/24
Re: [lmi] [Bulk] KVM performance [Was: Compiling takes longer with gcc-4.9.2], Greg Chicares, 2016/01/25
[lmi] cgicc changes [Was: Compiling takes longer with gcc-4.9.2], Greg Chicares, 2016/01/18