parsum and nbthreads

   Hi,

   I've recently used parsum(m2=1,20,<code>) on a 16-threaded
  machine. parsum parallelizes the sum only up to floor(sqrt(20))
  threads (hence 4 in my case, for a 16-threaded computer). While
  this is certainly a good limit if the number of things to sum is
  >= nbthreads^2, it is less good in the other case.

    Couldn't parsum limit the number of threads to something
  larger if b-a is small? I suspect accessing the number of threads
  from inside parsum() is off-limits. However one could use something
  similar to

min(N,sqrtint(N+90)),

  where N=b-a+1 (you get N threads up to N=10, then roughly
  sqrt(N)).

     Thoughts?

         Loïc

PS: it's easy to outsmart parsum, summing up to 256 and substituting
  <code> with if (m2<=20,<code>), however I think it'd be better if
  parsum were smarter.