Re: [eigen] Help on solving a race condition

[Gael Guennebaud <gael.guennebaud@xxxxxxxxx>]

On Fri, Jun 8, 2012 at 4:35 PM, Hauke Heibel
<hauke.heibel@xxxxxxxxxxxxxx> wrote:

> #pragma omp critical
> {
>  static std::ptrdiff_t m_l1CacheSize =
> manage_caching_sizes_helper(queryL1CacheSize(),8 * 1024);
>  static std::ptrdiff_t m_l2CacheSize =
> manage_caching_sizes_helper(queryTopLevelCacheSize(),1*1024*1024);
> }

yes that would work, but mutex introduces a too large overhead. This
function is called for every matrix product!

It seems OpenMP's support for atomics is not very good. I managed to
make helgrind happy with the following:

  static tbb::atomic<std::ptrdiff_t> m_l1CacheSize;
  static tbb::atomic<std::ptrdiff_t> m_l2CacheSize;
  if(!m_l1CacheSize)
  {
    std::ptrdiff_t l1 =
manage_caching_sizes_helper(queryL1CacheSize(),8 * 1024);
    m_l1CacheSize.fetch_and_store(l1);
  }
  if(!m_l2CacheSize)
  {
    std::ptrdiff_t l2 =
manage_caching_sizes_helper(queryTopLevelCacheSize(),1*1024 * 1024);
    m_l2CacheSize.fetch_and_store(l2);
  }

but 1) this requires Intel's TBB, 2) I still have to measure the
overhead of this solution.


best,
Gael.

gael.