We've noticed similar sorts of things. One possibility is that the loop in your test code is not aligned as well in one version. Or perhaps your stack is hitting the same location modulo 4096, which is a known issue on some modern processors. There might be SSE code in the linker and AVX code in the addmul_1 function. The kernel might pin the process to a different CPU which is slightly slower or faster, when the pthreads library is used. You might also hit some frequency scaling in the CPU due to the pthreads library taking longer to link in. There's so many possibilities on a modern CPU, it hardly bears thinking about.
Also, in your code, you don't seem to set y anywhere and I wasn't aware you could use 1e8 as an int constant. Bill. On 11 August 2017 at 18:10, Marcel Keller <m.kel...@bristol.ac.uk> wrote: > Hi, > > I've noticed that the performance of mpn_addmul_1 can depend considerably > on whether I link against libpthread, which strikes me as very weird: > > $ g++ -O3 Time-addmul_1.cpp ~/src/mpir-3.0.0-ivybridge/mpn/addmul_1.o -o > a.out > > $ g++ -O3 Time-addmul_1.cpp ~/src/mpir-3.0.0-ivybridge/mpn/addmul_1.o -o > b.out -lpthread > > $ ./a.out > mpn_addmul_1: 0.506279 > > $ ./b.out > mpn_addmul_1: 0.682086 > > Disassembling the binaries shows that the mpn function in > Time-addmul_1.cpp is compiled exactly the same way. > > I'm running CentOS 7 and GCC 6.2. The source as well as the outputs are > attached. > > Does anyone have any idea why this could be? > > Best regards, > Marcel > > -- > You received this message because you are subscribed to the Google Groups > "mpir-devel" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to mpir-devel+unsubscr...@googlegroups.com. > To post to this group, send email to mpir-devel@googlegroups.com. > Visit this group at https://groups.google.com/group/mpir-devel. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "mpir-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to mpir-devel+unsubscr...@googlegroups.com. To post to this group, send email to mpir-devel@googlegroups.com. Visit this group at https://groups.google.com/group/mpir-devel. For more options, visit https://groups.google.com/d/optout.
