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Some Notes about Hyper-Threading
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Wylie Garvin



Joined: 05 Jul 2007
Posts: 657
Location: Montreal, Canada
PostPost subject: Re: Some Notes about Hyper-Threading    Posted: Sun Dec 11, 2011 12:23 am Reply to topic Reply with quote
Trahald wrote:
I'm just left wondering whether i could expect any significant difference between leaving HT on and just using one thread per core, or disabling HT? I would have expected to see a small but insignificant difference, but the test results from Sedat, particularly the mate search test, seems quite startling. Thoughts here would be welcome.


One big issue here, is whether your operating system understands how to schedule threads properly for a hyperthreaded processor or not. From Sedat's screenshots, I'm guessing he is using Windows XP.

If you use Windows 7, its scheduler understands that putting two threads on the same physical core is not as good as putting each thread on its own physical core paired with nothing. But I don't know if the Windows XP scheduler was ever updated to handle this. (I read somewhere that the Windows 2000 scheduler wasn't, even though there were HT P4's back then). Even if the scheduler puts your 4 engine threads each on their own core, background processes might still be given timeslices on the "empty" half of one or more cores, slowing down the chess threads a bit.

Turning HT off in the bios will guarantee that your chess engine threads never have to share the resources of a physical core (particularly memory bandwidth and cache) with another thread. If you leave it on, there is no guarantee and you just have to hope your OS knows what its doing.
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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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