We REALLY nead a NON-PCH build in JPRT NOW!

[Stefan Karlsson]

On 2015-04-03 00:36, Kim Barrett wrote:
> On Apr 2, 2015, at 12:06 PM, Volker Simonis <volker.simonis at gmail.com> wrote:
>> while precompiled headers (PCH) are a nice and effective way of
>> improving hotspot build times
> Are we sure about that?

I'm sure that my full builds are faster with PCH, while others report 
the opposite.

These are the hotspot builds times I got a couple of months ago:
slowdebug
PCH
real    1m9.998s
user    12m0.437s
sys    1m56.291s

No PCH
real    1m27.170s
user    23m21.101s
sys    1m43.651s


product
PCH
real    1m19.933s
user    17m54.229s
sys    2m4.508s

No PCH
real    1m36.768s
user    28m9.931s
sys    1m46.288s

>
> Earlier today I ran into a local build failure that appeared to me to
> be possibly PCH-related.
>
> So I decided to try disabling PCH, since I now know about the option
> for doing so, from Volker's email.  But I wanted to see how much
> slower my build times would be.
>
> Imagine my surprise when disabling PCH made my clean builds 10-15%
> *faster*.  This is for a full jdk root "make images" build, which
> makes that much of a difference even more astonishing, because there's
> a lot more going on there than just compiling Hotspot.
>
> So how sure are we that PCH (or perhaps the way we are using it)
> provides any positive benefit at all?  I'm pretty sure it's not doing
> anything good for me.
>
> For reference, my build configuration is Ubuntu 14.04 x86_64,
> reporting 24 processors.  My configure options are
>
>    --enable-ccache
>    --with-debug-level=release
>    --disable-zip-debug-info
>    --disable-precompiled-headers     -- new
>    --with-jobs=24
>
> I made sure to clear the ccache between each build.

IIRC, running without ccache is usually faster for me.

StefanK