  Exploiting the performance of today's microprocessors requires intimate
knowledge of the microarchitecture as well as an awareness of the ever-growing
complexity in thread and cache topology. LIKWID is a set of command line
utilities that addresses four key problems: Probing the thread and cache
topology of a shared-memory node, enforcing thread-core affinity on a program,
measuring performance counter metrics, and microbenchmarking for reliable upper
performance bounds. Moreover, it includes a mpirun wrapper allowing for
portable thread-core affinity in MPI and hybrid MPI/threaded applications. To
demonstrate the capabilities of the tool set we show the influence of thread
affinity on performance using the well-known OpenMP STREAM triad benchmark, use
hardware counter tools to study the performance of a stencil code, and finally
show how to detect bandwidth problems on ccNUMA-based compute nodes.
