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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: Tue, 05 Jan 2016 03:19:45 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.3.0

On 2016-01-04 11:00, Vadim Zeitlin wrote:
> On Mon, 04 Jan 2016 02:59:23 +0000 Greg Chicares <address@hidden> wrote:
> GC> >  I've redone the benchmarks on a Linux machine (this is a notebook with 
> i7
> GC> > 4712HQ with 16GiB RAM and 1TB SSD) to compare the relative speed of
> GC> > compiling inside the VM and cross-compiling.
> GC> 
> GC> Is your VM...a msw-7 guest, in a vmware host?
>  Yes, I've simply cloned my existing VM that I previously used under MSW
> host and I'm using it now under Linux host with the (free (as the beer))
> VMware player.

I believe that explains why it's less painful for you than for me to build
in a VM: your guest is a 64-bit OS, while mine's 32-bit.

> GC> > wxMSW build             Time (s)        Size (MB)       CPU use (%)
> GC> > 
> =========================================================================
> GC> > MinGW 3.4.5             341               82
> GC> > Cygwin 4.9.2            424              463            637
> GC> > MinGW-w64 4.9.1         429              462
> GC> > Debian 4.9.1            322              567            629
> ...
> GC> > A half-surprise is that the native compiler is not faster than the
> GC> > Cygwin one on this machine, unlike in my previous tests and I'm not
> GC> > sure why is it so
> GC> 
> GC> That's so strange that I wonder whether the native and Cygwin compilers
> GC> were built with similar options. A wild guess: maybe the native one
> GC> targets a more conservative architecture, like i586.
>  Just to be clear, these are the same compilers, in the same VM, under a
> similar VM software just on a different host. I can't directly compare the
> times for the builds on different hardware, so I don't know if it means
> that VMware under MSW is "faster" or VMplayer under Linux is slower, but
> something outside the VM must be affecting this.

Thus, whether (MinGW-w64 native) beats (MinGW-w64 Cygwin cross compiler)
seems to depend on...well, who knows--maybe the hardware in your two
different hosts. But neither MinGW-w64 choice is universally faster.

People in the office are using 64-bit msw-7, so they'll probably see the
kind of speed difference you've reported (and not the far worse kind I've
reported for 32-bit msw-xp).

Your table above actually lists two different versions of MinGW-w64
(last digit '1' or '2'). We'll want to make sure we're all using the same
version. That's a conclusive argument against the cross-compilers that
Cygwin provides--they offer only one "current" and one "prior" version.

> GC> > Notice that it would also be worth using --without-opengl configure 
> option
> GC> > in either case as lmi doesn't wxGLCanvas, but this is a small gain.
> GC> 
> GC> But that's a small, safe change, so it's probably worthwhile.
>  Should I commit the addition of --without-opengl and
> --disable-precomp-headers to install_wx.make then or will you do it?

Committed 20160105T0146Z, revision 6463.

> GC> I haven't even tried cross-compiling lmi yet. It would be enormously 
> helpful
> GC> to me if you could figure out how to make that work.
>  I'll post my notes soon.

Thanks. There's one last set of changes we'll make to lmi, and once
that's done, we'll upgrade gcc.

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