Subject: Re: qrj

From: Rich Loft <[email-masked]>
Date: Thu, 29 Jun 2000 13:29:55 -0600 (MDT)

Ben:

   How much faster on the Compaq is the single node qrj (pure OMP) version
   say compared to the IBM?

   What scheduling policy are you using on the OMP DO PARALLEL?

   Likewise, how much faster is a single processor run of qrj
   on prospect?

   Have you made any progress in developing a standalone
   version of qrj that could be changed/studied readily in isolation?

   Unrolling transpositions means this: change

   do j=1,M
      do i=1,N
         a(j,i)=b(i,j)
      end do
   end do

   into

   do jj=1,M,Mblk
      do ii=1,N,Nblk
         do j=jj,MIN(jj-1+Mblk,M)
            do i=ii,MIN(ii-1+Nblk,N)
               a(j,i)=b(i,j)
            end do
         end do
      end do
   end do

   This tends to improve cache performance on many systems.

					      Kind regards,
   
                                              Rich

   Date: Thu, 29 Jun 2000 13:05:49 -0600 (MDT)
   From: Ben Foster <[email-masked]>
   Content-Length: 729

   Rich:

   Recall that my "improvements" to the qrj routine did not
   result in significant speedup on IBM or Origin, and maybe
   only 8% on the J90's. However, I've just run it on the
   Compaq prospect, with hybrid mpi/openmp, and with 12 procs 
   (3 nodes) it was faster than the old qrj code by better than 
   40%! With 24 procs (6 nodes) it also made very significant 
   speedup. It now appears to be faster than the Origin at
   both 12 and 24 procs.

   Prospect is the only system so far where I run hybrid mpi/openmp.
   Could this be the reason it responds so much better to this
   change? Or is it somehow less sensitive to load imbalance?

   Why do you think the Compaq would benefit from this change
   so much more than the other machines?

   --Ben