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Some Notes about Hyper-Threading
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Vincent Diepeveen



Joined: 09 Mar 2006
Posts: 1738
Location: The Netherlands
PostPost subject: Re: Some Notes about Hyper-Threading    Posted: Tue Dec 13, 2011 6:46 pm Reply to topic Reply with quote
bob wrote:
Werewolf wrote:
bob wrote:


Problem with HT on is that if you have 4 physical cores, and search X NPS, when you go to 8 cores (HT on) the tree will grow by 30%. If your NPS doesn't grow by MORE than 30%, you see a net loss.

NPS is NOT the way to measure parallel search performance. It provides completely bogus comparisons...


Your answer is too interesting to let it slip by!
a) Why does the tree grow by 30% with HT on?
b) Is this also true if we move from 4 physical cores to 8?
c) Why do the np/s have to increase by 30% or more to maintain performance? (because surely the HT tree isn't the same tree as the Non-HT tree and therefore time to depth is misleading)


That assumes that if you have 4 real cores, and you test with 4 threads, and then use 8 logical cores (HT on) and rul with 8 threads, then the tree will grow about 30% in size due to the parallel search overhead.

alpha/beta is a purely sequential algorithm as defined. You need to establish a bound at each node, by searching the best move first, then you use that bound to search the remaining nodes more efficiently. When you don't do this (and you can't in a parallel search) you search a larger tree to reach the same depth..

For (b) yes. It is not a "core" issue but a "number of threads" issue.

(c) think about it. Going from 4 to 8 threads makes the tree 30% larger. If you don't speed up enough with the extra 4 threads to offset that loss, you see a net decrease in performance. If the NPS increases by more than that amount, you see a (small) net gain.


Hi Bob,

If your speedup is 3.1 out of 4 and 30% is the break even point moving to 8 cores for hyperthreading, then that would mean that crafty's speedup deteriorates a lot namely that it's break even at:

Assuming 100% scaling now: 4 * 1.3 = 5.2
So you get less than 3.1 out of 5.2 with 5.2 being what you get at 8 cores.

8 * 3.1 / 5.2 = 4.76 out of 8

So if even 30% increase in nps by hyperthreading doesn't benefit
crafty then that means that assuming you get 3.1 out of 4 as a speedup,
that at 8 cores you get 4.76 out of 8.

For Young Brother Wait that seems like a rather small speedup out of 8 cores to me.

Vincent
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Subject Author Date/Time
Some Notes about Hyper-Threading Sedat Canbaz Fri Dec 09, 2011 3:50 pm
      Re: Some Notes about Hyper-Threading Ernest Bonnem Sat Dec 10, 2011 12:31 am
            Re: Some Notes about Hyper-Threading Sedat Canbaz Sat Dec 10, 2011 2:43 am
                  Re: Some Notes about Hyper-Threading Robert Hyatt Sat Dec 10, 2011 4:06 pm
                        Re: Some Notes about Hyper-Threading enrico fagiuoli Sat Dec 10, 2011 11:26 pm
                        Re: Some Notes about Hyper-Threading Ernest Bonnem Mon Dec 12, 2011 8:07 pm
                        Re: Some Notes about Hyper-Threading H.G.Muller Tue Jun 26, 2012 4:30 pm
                              Re: Some Notes about Hyper-Threading Daniel Shawul Tue Jun 26, 2012 11:35 pm
                                    Re: Some Notes about Hyper-Threading H.G.Muller Wed Jun 27, 2012 5:40 am
                                          Re: Some Notes about Hyper-Threading Daniel Shawul Wed Jun 27, 2012 10:23 am
                                                Re: Some Notes about Hyper-Threading H.G.Muller Wed Jun 27, 2012 10:57 am
                                                      Re: Some Notes about Hyper-Threading Daniel Shawul Wed Jun 27, 2012 11:33 am
                  Re: Some Notes about Hyper-Threading Ernest Bonnem Sun Dec 11, 2011 1:19 am
                        Re: Some Notes about Hyper-Threading M ANSARI Sun Dec 11, 2011 6:06 am
                              Re: Some Notes about Hyper-Threading Sedat Canbaz Mon Dec 12, 2011 11:14 am
                        Re: Some Notes about Hyper-Threading Sedat Canbaz Sun Dec 11, 2011 8:31 am
                              Re: Some Notes about Hyper-Threading Ernest Bonnem Sun Dec 11, 2011 6:00 pm
                                    Re: Some Notes about Hyper-Threading Vincent Diepeveen Sun Dec 11, 2011 7:12 pm
                                          Re: Some Notes about Hyper-Threading Vincent Diepeveen Sun Dec 11, 2011 7:35 pm
                                                Re: Some Notes about Hyper-Threading Sedat Canbaz Mon Dec 12, 2011 2:03 am
                                                      Re: Some Notes about Hyper-Threading Vincent Lejeune Mon Dec 12, 2011 8:46 am
                                                            Re: Some Notes about Hyper-Threading Sedat Canbaz Mon Dec 12, 2011 12:04 pm
                                                                  Re: Some Notes about Hyper-Threading Vincent Lejeune Mon Dec 12, 2011 12:32 pm
                                    Re: Some Notes about Hyper-Threading Sedat Canbaz Mon Dec 12, 2011 2:37 am
                                          Re: Some Notes about Hyper-Threading Ernest Bonnem Mon Dec 12, 2011 5:24 pm
                                                Re: Some Notes about Hyper-Threading Sedat Canbaz Mon Dec 12, 2011 6:14 pm
                                                      Re: Some Notes about Hyper-Threading Robert Hyatt Mon Dec 12, 2011 6:51 pm
                                                            Re: Some Notes about Hyper-Threading Sedat Canbaz Mon Dec 12, 2011 7:27 pm
                                                                  Re: Some Notes about Hyper-Threading Robert Hyatt Tue Dec 13, 2011 5:01 pm
                                                      Re: Some Notes about Hyper-Threading Vincent Lejeune Tue Dec 13, 2011 2:10 am
                                                            Re: Some Notes about Hyper-Threading Sedat Canbaz Tue Dec 13, 2011 8:35 am
                                                            Re: Some Notes about Hyper-Threading Sujay Jagannathan Wed Jun 27, 2012 12:42 pm
                                                      Re: Some Notes about Hyper-Threading Vincent Lejeune Tue Jun 26, 2012 4:00 pm
                                                            Re: Some Notes about Hyper-Threading Sedat Canbaz Tue Jun 26, 2012 4:56 pm
                                                                  Re: Some Notes about Hyper-Threading Vincent Lejeune Wed Jun 27, 2012 7:45 am
                                                                  Re: Some Notes about Hyper-Threading Vincent Lejeune Wed Jun 27, 2012 10:22 pm
                                                Re: Some Notes about Hyper-Threading Sedat Canbaz Mon Dec 12, 2011 7:51 pm
      Re: Some Notes about Hyper-Threading Rodolfo Leoni Sat Dec 10, 2011 10:45 am
            Re: Some Notes about Hyper-Threading Sedat Canbaz Sat Dec 10, 2011 12:25 pm
                  Re: Some Notes about Hyper-Threading Albert Silver Sat Dec 10, 2011 12:33 pm
                        Re: Some Notes about Hyper-Threading Vincent Diepeveen Sat Dec 10, 2011 7:52 pm
                              Re: Some Notes about Hyper-Threading Sedat Canbaz Sat Dec 10, 2011 10:23 pm
                                    Re: Some Notes about Hyper-Threading Russell Murray Sat Dec 10, 2011 11:58 pm
                                          Re: Some Notes about Hyper-Threading Wylie Garvin Sun Dec 11, 2011 12:23 am
                                                Re: Some Notes about Hyper-Threading Robert Hyatt Sun Dec 11, 2011 12:38 am
                                    Re: Some Notes about Hyper-Threading Vincent Diepeveen Sun Dec 11, 2011 4:25 pm
                  Re: Some Notes about Hyper-Threading Robert Hyatt Sat Dec 10, 2011 4:04 pm
                        Re: Some Notes about Hyper-Threading Rodolfo Leoni Sat Dec 10, 2011 8:53 pm
                              Re: Some Notes about Hyper-Threading Robert Hyatt Sun Dec 11, 2011 12:36 am
                                    Re: Some Notes about Hyper-Threading Rodolfo Leoni Sun Dec 11, 2011 2:19 pm
                                          Re: Some Notes about Hyper-Threading Robert Hyatt Sun Dec 11, 2011 3:49 pm
                                    Re: Some Notes about Hyper-Threading Sujay Jagannathan Wed Jun 27, 2012 12:36 pm
                              Re: Some Notes about Hyper-Threading Robert Flesher Sun Dec 11, 2011 7:00 pm
                                    Re: Some Notes about Hyper-Threading Vincent Diepeveen Sun Dec 11, 2011 7:27 pm
                              Re: Some Notes about Hyper-Threading Lonnie Cook Wed Jun 27, 2012 12:44 pm
                        Re: Some Notes about Hyper-Threading Carl Bicknell Mon Dec 12, 2011 9:06 am
                              Re: Some Notes about Hyper-Threading Robert Hyatt Mon Dec 12, 2011 1:31 pm
                                    Re: Some Notes about Hyper-Threading Carl Bicknell Mon Dec 12, 2011 4:00 pm
                                          Re: Some Notes about Hyper-Threading Robert Hyatt Mon Dec 12, 2011 4:31 pm
                                                Re: Some Notes about Hyper-Threading Carl Bicknell Mon Dec 12, 2011 4:54 pm
                                                      Re: Some Notes about Hyper-Threading Robert Hyatt Mon Dec 12, 2011 6:42 pm
                                                            Re: Some Notes about Hyper-Threading Robert Flesher Tue Dec 13, 2011 4:25 am
                                    Re: Some Notes about Hyper-Threading Vincent Diepeveen Tue Dec 13, 2011 6:46 pm
                                          Re: Some Notes about Hyper-Threading Robert Hyatt Wed Dec 14, 2011 4:30 am
                                                Re: Some Notes about Hyper-Threading Sedat Canbaz Wed Dec 14, 2011 1:01 pm
                                                      Re: Some Notes about Hyper-Threading Robert Hyatt Wed Dec 14, 2011 7:35 pm
                                                            Re: Some Notes about Hyper-Threading Sedat Canbaz Wed Dec 14, 2011 8:22 pm
                                                      Re: Some Notes about Hyper-Threading Sedat Canbaz Wed Dec 14, 2011 7:39 pm
                                                            Re: Some Notes about Hyper-Threading Robert Hyatt Wed Dec 14, 2011 10:43 pm
                                                                  Re: Some Notes about Hyper-Threading Sedat Canbaz Thu Dec 15, 2011 2:21 am
                                                                        Re: Some Notes about Hyper-Threading Robert Hyatt Fri Dec 16, 2011 5:31 pm
                                                                              Re: Some Notes about Hyper-Threading Sedat Canbaz Fri Dec 16, 2011 6:55 pm
                                                                                    Re: Some Notes about Hyper-Threading Robert Hyatt Sat Dec 17, 2011 3:52 pm
                                                                  Re: Some Notes about Hyper-Threading Sedat Canbaz Thu Dec 15, 2011 2:34 am
                                                                        Re: Some Notes about Hyper-Threading Sedat Canbaz Thu Dec 15, 2011 3:13 am
                                                                              Re: Some Notes about Hyper-Threading Sedat Canbaz Fri Dec 16, 2011 11:27 am
                                                                                    Re: Some Notes about Hyper-Threading Sedat Canbaz Fri Dec 16, 2011 12:19 pm
                                                                                    Re: Some Notes about Hyper-Threading Robert Hyatt Fri Dec 16, 2011 11:25 pm
                                                                                          Re: Some Notes about Hyper-Threading Sedat Canbaz Sat Dec 17, 2011 12:26 am
                                                                                          Re: Some Notes about Hyper-Threading Sedat Canbaz Sat Dec 17, 2011 1:27 am
                                                                                          Re: Some Notes about Hyper-Threading Robert Hyatt Sat Dec 17, 2011 4:50 am
                                                                                          Re: Some Notes about Hyper-Threading Robert Hyatt Sat Dec 17, 2011 4:49 am
                                                                                          Re: Some Notes about Hyper-Threading Sedat Canbaz Sat Dec 17, 2011 10:11 am
                                                                                          Re: Some Notes about Hyper-Threading Robert Hyatt Sat Dec 17, 2011 3:54 pm
                                                                              Re: Some Notes about Hyper-Threading Robert Hyatt Fri Dec 16, 2011 11:23 pm
                                                                                    Re: Some Notes about Hyper-Threading Sedat Canbaz Sat Dec 17, 2011 12:09 am
                                                                                          Re: Some Notes about Hyper-Threading Robert Hyatt Sat Dec 17, 2011 4:52 am
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