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 users@lists.fedoraproject.org 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.
No, I do not use such options
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