On Wed, Nov 13, 2024 at 11:21:46PM +0100, Patrick Dupre wrote:
> > Subject: Re: gcc/gsl
> >
> > On Wed, Nov 13, 2024 at 10:50:38PM +0100, Patrick Dupre via users wrote:
> > > >
> > > > > On 13 Nov 2024, at 18:33, Patrick Dupre via users
> > > > > <[email protected]> wrote:
> > > > >
> > > > > Why this behavior?
> > > >
> > > > Do both versions produce the same results when copied to the other
> > > > machine?
> > > The results depends on the machine which has compiled the code, not on
> > > the machine
> > > where the code is run.
> > >
> > > Is there a way to specify the architecture i7 or i5 ?
> >
> > i7 vs. i5 don't mean anything for the compiler, the set of ISAs those CPUs
> > support and their generation is what matters.
> > Though, unless you compile with -march=native or -mcpu=native (or unless the
> > build system of the projects injects compiler flags depending on the current
> > CPU), the CPU on which you compile it shouldn't affect the flags with which
> > the code is compiled and same compiler + same source + same command line
> > flags should result in identical assembly.
> > If you are using -march=native or -mcpu=native, you've asked for it, you can
> > then use
> > gcc -march=native -v -S -xc /dev/null -o /dev/null 2>&1 | grep cc1
> > to print what exact flags does that turn.
You didn't tell if you are actually using -march=native or -mcpu=native
in the gsl compilation or not.
> on i5
> /usr/libexec/gcc/x86_64-redhat-linux/14/cc1 -quiet -v /dev/null
> -march=skylake -mmmx -mpopcnt -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2
> -mavx -mavx2 -mno-sse4a -mno-fma4 -mno-xop -mfma -mno-avx512f -mbmi -mbmi2
> -maes -mpclmul -mno-avx512vl -mno-avx512bw -mno-avx512dq -mno-avx512cd
> -mno-avx512vbmi -mno-avx512ifma -mno-avx512vpopcntdq -mno-avx512vbmi2
> -mno-gfni -mno-vpclmulqdq -mno-avx512vnni -mno-avx512bitalg -mno-avx512bf16
> -mno-avx512vp2intersect -mno-3dnow -madx -mabm -mno-cldemote -mclflushopt
> -mno-clwb -mno-clzero -mcx16 -mno-enqcmd -mf16c -mfsgsbase -mfxsr -mno-hle
> -msahf -mno-lwp -mlzcnt -mmovbe -mno-movdir64b -mno-movdiri -mno-mwaitx
> -mno-pconfig -mno-pku -mprfchw -mno-ptwrite -mno-rdpid -mrdrnd -mrdseed
> -mno-rtm -mno-serialize -msgx -mno-sha -mno-shstk -mno-tbm -mno-tsxldtrk
> -mno-vaes -mno-waitpkg -mno-wbnoinvd -mxsave -mxsavec -mxsaveopt -mxsaves
> -mno-amx-tile -mno-amx-int8 -mno-amx-bf16 -mno-uintr -mno-hreset -mno-kl
> -mno-widekl -mno-avxvnni -mno-avx512fp16 -mno-avxifma -mno-avxvnniint8
> -mno-avxneconvert -mno-cmpccxadd -mno-amx-fp16 -mno-prefetchi -mno-raoint
> -mno-amx-complex -mno-avxvnniint16 -mno-sm3 -mno-sha512 -mno-sm4 -mno-apxf
> -mno-usermsr --param l1-cache-size=32 --param l1-cache-line-size=64 --param
> l2-cache-size=12288 -mtune=skylake -quiet -dumpbase null -version -o /dev/null
>
> on i7
> /usr/libexec/gcc/x86_64-redhat-linux/14/cc1 -quiet -v /dev/null
> -march=skylake -mmmx -mpopcnt -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2
> -mavx -mavx2 -mno-sse4a -mno-fma4 -mno-xop -mfma -mno-avx512f -mbmi -mbmi2
> -maes -mpclmul -mno-avx512vl -mno-avx512bw -mno-avx512dq -mno-avx512cd
> -mno-avx512vbmi -mno-avx512ifma -mno-avx512vpopcntdq -mno-avx512vbmi2
> -mno-gfni -mno-vpclmulqdq -mno-avx512vnni -mno-avx512bitalg -mno-avx512bf16
> -mno-avx512vp2intersect -mno-3dnow -madx -mabm -mno-cldemote -mclflushopt
> -mno-clwb -mno-clzero -mcx16 -mno-enqcmd -mf16c -mfsgsbase -mfxsr -mno-hle
> -msahf -mno-lwp -mlzcnt -mmovbe -mno-movdir64b -mno-movdiri -mno-mwaitx
> -mno-pconfig -mno-pku -mprfchw -mno-ptwrite -mno-rdpid -mrdrnd -mrdseed
> -mno-rtm -mno-serialize -msgx -mno-sha -mno-shstk -mno-tbm -mno-tsxldtrk
> -mno-vaes -mno-waitpkg -mno-wbnoinvd -mxsave -mxsavec -mxsaveopt -mxsaves
> -mno-amx-tile -mno-amx-int8 -mno-amx-bf16 -mno-uintr -mno-hreset -mno-kl
> -mno-widekl -mno-avxvnni -mno-avx512fp16 -mno-avxifma -mno-avxvnniint8
> -mno-avxneconvert -mno-cmpccxadd -mno-amx-fp16 -mno-prefetchi -mno-raoint
> -mno-amx-complex -mno-avxvnniint16 -mno-sm3 -mno-sha512 -mno-sm4 -mno-apxf
> -mno-usermsr --param l1-cache-size=32 --param l1-cache-line-size=64 --param
> l2-cache-size=6144 -mtune=skylake -quiet -dumpbase null -version -o /dev/null
The difference is just --param l2-cache-size=X value, that can affect just
loop prefetching.
Jakub
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