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

Stefan Karlsson stefan.karlsson at oracle.com
Fri Apr 3 06:36:09 UTC 2015

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:
real    1m9.998s
user    12m0.437s
sys    1m56.291s

real    1m27.170s
user    23m21.101s
sys    1m43.651s

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

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.


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