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[pinkenburg <pinkenburg AT bnl.gov>]

Hi Johannes,

Thanks a lot - this is what I was looking for. That'll put gcc 15 on the 
back burner for the time being. I had the feeling it sounded too good to 
be true (for sPHENIX) :)

Chris

On 10/27/2025 8:57 AM, Johannes Elmsheuser (via phys-npps-members-l 
Mailing List) wrote:
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> Hi Chris,
>
> in ATLAS we have since a while dev3LCG Athena offline nightlies with 
> gcc14 and gcc15 - dev3LCG means here that the current ROOT head 
> version is used - the gcc15 nightly is in addition compiled with C++23 
> standard compared to the C++20 standard default with gcc14 - but we 
> are not using any C++23 features yet - there are no other compilation 
> optimizations used apart from the x86_64_v2 micro architecture by 
> default. Our default gcc14 nightly uses ROOT 6.36/02 a few other 
> "older" versions of some externals.
>
> My unscientific quick test in running 3 times in a row a 
> data22_13p6TeV RAW data reconstruction (8 threads) followed by a 
> derivation production (8 processes) on 1100 events using these gcc14 
> and gcc15 nightlies showed that the gcc15 nightly on a 64 threads AMD 
> EPYC 7302 bare metal machine is very slightly slower in the walltime 
> for both workflows - our default gcc14 nightly is slightly faster than 
> both of the dev3LCG nightlies. We have another special nightly which 
> uses the x86_64_v3 micro architecture compilation flag for the Athena 
> stack (but not LCG or the OS), but we don't see any gains here so far.
>
> I did not test a Geant4 workflow.
>
> Side note: there is a claim that with EL10 that is compiled with 
> x86_64_v3 micro architecture by default (so the full stack) there will 
> be some performance gain of a few percent by default.
>
> Cheers, Johannes
>
> On 10/26/25 5:03 PM, pinkenburg wrote:
> > Hi folks,
> >
> > I see claims that gcc 15 produces significantly faster binaries than 
> > gcc 14 (in some cases 20%). Does anybody have experience how gcc 15 
> > performs with our use cases (event reconstruction, simulations)? I 
> > don't want to go through this effort if there isn't a large enough 
> > carrot on the other side.
> >
> > Thanks
> > Chris

--
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Christopher H. Pinkenburg       ;    pinkenburg AT bnl.gov
                                ;    http://www.phenix.bnl.gov/~pinkenbu

Brookhaven National Laboratory  ;    phone: (631) 344-5692
Physics Department Bldg 510 C   ;    fax:   (631) 344-3253
Upton, NY 11973-5000

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