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YBWC: Active Reparenting
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Daniel Shawul



Joined: 14 Mar 2006
Posts: 2185
Location: Ethiopia
PostPost subject: Re: YBWC: Active Reparenting    Posted: Wed Apr 11, 2012 12:14 pm Reply to topic Reply with quote
Rein Halbersma wrote:
mcostalba wrote:
In Young Brothers Wait Concept (YBWC) available slaves are booked by the split point master, then start to search below the assigned split point and, once finished, return in idle state waiting to be booked by another master.

I have pushed a patch that introduces what I have called "Active Reparenting" so that when a slave finishes its job on the assigned split point, instead of passively waiting to be booked, searches a suitable active split point and reparents itself to that split point. Then immediately starts to search below the split point in exactly the same way of the others split point's slaves. This reduces to zero the time waiting in idle loop and _could_ increase scalability especially with many (8 or more) cores, at least this is the idea.

Perhaps Don Dailey can comment on this further, but it seems like you have rediscovered "randomized work stealing"! The MIT Cilk project used such a provably optimal scheduler to implement CilkChess. More speculatively: I wouldn't be surprised if even the convoluted DTS-type scheduling of the YBW algorithm would be another manifestation of work stealing.

What he did is not randomized work stealing, there is nothing random there. He just checked existing split points to reattach itself.
This will most probably not decreases idle time because working threads pick up threads quickly anyway if you let them, but the selection made by the former i.e higher up
in the tree may help. I actually mentioned about the randomized work stealing that I use on cluster search in my first post.
But this might not be the smartest thing to do since we could have differnt network interfaces with varying latency. MPI allows you to group processors for most efficient work sharing.

Cilk begins with an overhead of creating and destryoing threads,as Vincent explained. I don't know if it keeps a thread pool
for that but it is still expensive anyway. For simple applications like parallel fibonacci serial versions outperform parallel versions due
to this overhead. OpenMP has added task based parallelism now but its performance is poor compared to Cilk. http://myxman.org/dp/node/182

Also from what I read the performance of Socrates chess is affected by this overhead too. The authors have blamed the poor performance
on the algorithm used (Jamboree search) but that seems to me very similar to YBW algorithm. http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TM-548.pdf
A speedup of 48 out of 256 is what they get and I also read somewhere eles not many extensions/reductions were used.
So I have my doubts about cilk eventhough it makes life a lot easier.
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Display posts from previous:   
Subject Author Date/Time
YBWC: Active Reparenting Marco Costalba Tue Apr 10, 2012 5:38 pm
      Re: YBWC: Active Reparenting Vincent Diepeveen Tue Apr 10, 2012 6:23 pm
            Re: YBWC: Active Reparenting Daniel Shawul Tue Apr 10, 2012 7:11 pm
                  Re: YBWC: Active Reparenting Vincent Diepeveen Tue Apr 10, 2012 7:54 pm
                        Re: YBWC: Active Reparenting Marco Costalba Tue Apr 10, 2012 8:48 pm
                              Re: YBWC: Active Reparenting Vincent Diepeveen Wed Apr 11, 2012 10:09 am
                                    Re: YBWC: Active Reparenting Robert Hyatt Mon Apr 16, 2012 6:53 pm
                        Re: YBWC: Active Reparenting Daniel Shawul Tue Apr 10, 2012 11:11 pm
                              Re: YBWC: Active Reparenting Daniel Shawul Tue Apr 10, 2012 11:33 pm
                              Re: YBWC: Active Reparenting Robert Hyatt Mon Apr 16, 2012 7:07 pm
                                    Re: YBWC: Active Reparenting Vincent Diepeveen Mon Apr 16, 2012 8:55 pm
                                          Re: YBWC: Active Reparenting Robert Hyatt Tue Apr 17, 2012 2:54 pm
                                                Re: YBWC: Active Reparenting Daniel Shawul Tue Apr 17, 2012 5:42 pm
                                                      Re: YBWC: Active Reparenting Robert Hyatt Tue Apr 17, 2012 8:01 pm
                                                            Re: YBWC: Active Reparenting Daniel Shawul Tue Apr 17, 2012 9:34 pm
                                                                  Re: YBWC: Active Reparenting Robert Hyatt Tue Apr 17, 2012 9:46 pm
                                                                        Re: YBWC: Active Reparenting Daniel Shawul Tue Apr 17, 2012 10:30 pm
                                                                              Re: YBWC: Active Reparenting Vincent Diepeveen Tue Apr 17, 2012 11:43 pm
                                                                                    Re: YBWC: Active Reparenting Daniel Shawul Wed Apr 18, 2012 1:05 am
                                                                                          Re: YBWC: Active Reparenting Vincent Diepeveen Wed Apr 18, 2012 11:24 am
                                                                                          Re: YBWC: Active Reparenting Daniel Shawul Wed Apr 18, 2012 1:01 pm
                                                                              Re: YBWC: Active Reparenting Robert Hyatt Wed Apr 18, 2012 7:34 pm
                                                                                    Re: YBWC: Active Reparenting Daniel Shawul Wed Apr 18, 2012 11:18 pm
                                                                                          Re: YBWC: Active Reparenting Vincent Diepeveen Thu Apr 19, 2012 7:01 am
                                                                                          Re: YBWC: Active Reparenting Daniel Shawul Thu Apr 19, 2012 12:46 pm
                                                                                          Re: YBWC: Active Reparenting Vincent Diepeveen Thu Apr 19, 2012 2:40 pm
                                                                                          Re: YBWC: Active Reparenting Daniel Shawul Thu Apr 19, 2012 9:32 pm
                                                                                          Re: YBWC: Active Reparenting Robert Hyatt Thu Apr 19, 2012 7:08 pm
                                                                                          Re: YBWC: Active Reparenting Daniel Shawul Thu Apr 19, 2012 9:37 pm
                                                                                          Re: YBWC: Active Reparenting Robert Hyatt Thu Apr 19, 2012 9:48 pm
                                                                                          Re: YBWC: Active Reparenting Robert Hyatt Thu Apr 19, 2012 6:59 pm
                                                                                          Re: YBWC: Active Reparenting Robert Hyatt Thu Apr 19, 2012 5:30 pm
                                                                        Re: YBWC: Active Reparenting Vincent Diepeveen Tue Apr 17, 2012 11:29 pm
                                                                              Re: YBWC: Active Reparenting Daniel Shawul Wed Apr 18, 2012 12:58 am
                                                                  Re: YBWC: Active Reparenting Vincent Diepeveen Tue Apr 17, 2012 11:18 pm
                                    Re: YBWC: Active Reparenting Daniel Shawul Tue Apr 17, 2012 5:37 pm
      Re: YBWC: Active Reparenting Álvaro Begué Tue Apr 10, 2012 6:27 pm
            Re: YBWC: Active Reparenting Vincent Diepeveen Tue Apr 10, 2012 6:44 pm
      Re: YBWC: Active Reparenting Robert Hyatt Tue Apr 10, 2012 9:39 pm
            Re: YBWC: Active Reparenting Marco Costalba Wed Apr 11, 2012 6:06 am
                  Re: YBWC: Active Reparenting Robert Hyatt Thu Apr 12, 2012 1:20 am
                        Re: YBWC: Active Reparenting Vincent Diepeveen Sun Apr 15, 2012 10:04 am
                              Re: YBWC: Active Reparenting Marco Costalba Sun Apr 15, 2012 10:22 am
                                    Re: YBWC: Active Reparenting Vincent Diepeveen Sun Apr 15, 2012 2:39 pm
                                          Re: YBWC: Active Reparenting Marco Costalba Mon Apr 16, 2012 5:29 am
                                                Re: YBWC: Active Reparenting Vincent Diepeveen Mon Apr 16, 2012 5:54 pm
                                                      Re: YBWC: Active Reparenting Marco Costalba Tue Apr 17, 2012 11:30 am
                                                Re: YBWC: Active Reparenting Marco Costalba Wed Apr 18, 2012 6:31 am
      Re: YBWC: Active Reparenting Rein Halbersma Wed Apr 11, 2012 7:23 am
            Re: YBWC: Active Reparenting Vincent Diepeveen Wed Apr 11, 2012 9:07 am
            Re: YBWC: Active Reparenting Vincent Diepeveen Wed Apr 11, 2012 9:31 am
            Re: YBWC: Active Reparenting Daniel Shawul Wed Apr 11, 2012 12:14 pm
                  Re: YBWC: Active Reparenting Vincent Diepeveen Wed Apr 11, 2012 1:54 pm
                  Re: YBWC: Active Reparenting Robert Hyatt Thu Apr 12, 2012 1:28 am
                        Re: YBWC: Active Reparenting Daniel Shawul Tue Apr 17, 2012 5:49 pm
                              Re: YBWC: Active Reparenting Vincent Diepeveen Tue Apr 17, 2012 11:10 pm
                                    Re: YBWC: Active Reparenting Daniel Shawul Wed Apr 18, 2012 12:50 am
                              Re: YBWC: Active Reparenting Robert Hyatt Wed Apr 18, 2012 7:38 pm
                                    Re: YBWC: Active Reparenting Daniel Shawul Wed Apr 18, 2012 11:30 pm
                                          Re: YBWC: Active Reparenting Vincent Diepeveen Thu Apr 19, 2012 7:08 am
                                                Re: YBWC: Active Reparenting Daniel Shawul Thu Apr 19, 2012 12:15 pm
                                                      Re: YBWC: Active Reparenting Vincent Diepeveen Thu Apr 19, 2012 1:53 pm
                                          Re: YBWC: Active Reparenting Robert Hyatt Thu Apr 19, 2012 7:11 pm
      Re: GPUs Srdja Matovic Mon Jun 04, 2012 5:08 pm
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