Package: libopenblas-base Version: 0.1.1-5 Severity: normal By default, OpenBLAS enables processor affinity on Linux-based systems, which binds the threads to fixed CPUs. This appropriate only for process execution on dedicated machine, and is not appropriate for general usage. For example, if two programs linked with OpenBLAS are both running, then the processor affinity will cause them to "fight" over the same CPUs, even if the system has enough CPUs to run both programs in parallel.
Suggestion: compile OpenBLAS with the NO_AFFINITY=1 flag, which disables processor affinity. In a situation where you *do* have a dedicated machine running the OpenBLAS program, disabling affinity causes a slight performance degradation. However, in that case the user can always re-enable affinity by using the taskset program. The converse is not true -- there does not seem to be any way to disable processor affinity in OpenBLAS if it is compiled in, and in any case disabling processor affinity is a more sensible default. Regards, Steven G. Johnson PS. You probably also want to set the maximum number of threads in OpenBLAS by compiling with the NUM_THREADS=xxx flag. Otherwise, the maximum number of threads is set by the number of cores of the build host, which is clearly wrong for Debian. Probably xxx=64 is a reasonable maximum these days -- this number only sets an upper bound on the number of threads used at runtime, since the actual number of cores is detected at runtime, and there seems only to be a slight memory penalty in buffer space for setting the maximum to be too large. Also, it looks like the code may have a hard-coded upper bound of 64 threads anyway (see init.c). -- System Information: Debian Release: 6.0.5 APT prefers stable APT policy: (500, 'stable') Architecture: amd64 (x86_64) Kernel: Linux 2.6.32-5-amd64 (SMP w/16 CPU cores) Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/bash -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
