Of course if you are using an AMD processor, surely it is a "performance marginality problem". :-)
Bill. On 11 August 2017 at 20:00, Bill Hart <goodwillh...@googlemail.com> wrote: > 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.
