Bernd, Yes I did that. Perhaps the app you ran in CPU 3 was susceptible to the timing issues. I looked for incorrect calculation or program logic results without regard to timing. tim -----Original Message----- From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf Of Bernd Harzog Sent: Friday, October 01, 2004 10:38 AM To: thin@xxxxxxxxxxxxx Subject: [THIN] Re: Hyperthreading Tim, Have the run the test that I alluded to? Fire up a rogue process that is isolated to CPU 3, and that only is allowed to run on CPU 3. My tests Windows 2000 MetaFrame XP server that was a clone of a production server at a major healthcare organization, shows that that one process running on CPU 3 rendered the whole server unusable. Running that process on CPU's 0 or 1 had no discernable effect. Cheers, Bernd Harzog CTO RTO Software, Inc. bernd.harzog@xxxxxxxxxxx 678-455-5506 x701 www.rtosoft.com -----Original Message----- From: Tim Mangan [mailto:tmangan@xxxxxxxxxxxx] Sent: Friday, October 01, 2004 10:25 AM To: thin@xxxxxxxxxxxxx Subject: [THIN] Re: Hyperthreading Although at times I have seen behavior that made me suspicious that one or the other of the logical processors (as in the 0,2 pair or 1,3) is "different", I have been unable to prove that out in tests when I try to nail it down. I believe that both logical processors are essentially identical, both from an Intel and a Microsoft point of view on Win2k. The only thing Microsoft will do differently on Win2k is that occasionally the threading algorithm will select a lower numbered processor (sort of like the third tie-breaker for making the playoffs). This may explain why it at times may seem to be unbalanced. To the best of my knowledge all that happens is that if one (either) of the logicals of a pair goes idle, some on-chip caching may be lost on it's other half. I suspect that this alters timing in that process as opposed to corrupting anything. I have never seen corruption at the chip level and believe me I looked! This makes sense in what we see in tests. Tim Mangan -----Original Message----- From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf Of Bernd Harzog Sent: Thursday, September 30, 2004 12:18 PM To: thin@xxxxxxxxxxxxx Subject: [THIN] Re: Hyperthreading Let me add some fuel to the fire. I do not know if this is pervasive, but I have noticed on several customer systems. On a hyperthreaded dual, you have processors 0,1,2 and 3. 0 and 1 are the "physical" processors, and 2 and 3 are the virtual processors. These four processors DO NOT behave identically. Specifically, the virtual processors seem to have severe problems with them that can negatively the performance of the whole server. Here is what we have observed. TScale has a feature that allows you to set the Affinity of a process. If you have an infrequently used process that tends to go rogue, we recommend that you consider putting in a Priority rule for that process to have its Priority be reduced when the process goes rogue, and then also nailing all instances of that infrequently used process to one of the N CPU's. That way, if two instances of that process are launched and go rogue they can be isolated to one of the NT CPU's and set to low priority so that they do not do damage to even that CPU. The problem that we observed is that when you set Priority rules in TScale they typically take the form of "reduce Priority when processname.exe uses X% CPU for more than N seconds". So, it might say, reduce the Priority of Acread32.exe when it takes more than 20% of CPU for 20 seconds. The theory is that it might validly need lots of CPU for 20 seconds, but if it is doing more than that, it is a hog and steps need to be taken to make sure that it does not harm other processes and users. Well what we discovered is that when a process is running on one of the virtual CPU's (2 or 3) and goes rogue, it shuts down the whole server. So, if something uses 25% of CPU (all of CPU 2 or 3) doing this on a virtual CPU on Windows 2000 somehow clogs up the entire system. So, our recommendations were; 1) don't use hyperthreading on Windows 2000, and if you insist upon turning it on, don't use Affinity to assign any processes to the virtual CPU's (only assign processes to the physical ones). I would be interested in knowing if anyone else has seen anything like this. If you have, and you could share with the list that would be most useful. Best Regards, Bernd Harzog CTO RTO Software, Inc. bernd.harzog@xxxxxxxxxxx 678-455-5506 x701 www.rtosoft.com -----Original Message----- From: Brian Madden [mailto:brian@xxxxxxxxxxxxxxx] Sent: Thursday, September 30, 2004 11:34 AM To: thin@xxxxxxxxxxxxx Subject: [THIN] Re: Hyperthreading The main problems in W2K with Hyperthreading are: (1) Stability. I haven't seen this personally, but it's something that everyone says (2) W2K doesn't realize that 4 hyperthreaded processors are really two physical processors. The problem is that the system might try to "load balance" some work evenly across processors 0 and 1, thinking it's doing a good job but not realizing that they're really going to the same place, all while procs 2 and 3 are sitting idle. Multiply this by several billion ticks per second and it could in theory lead to worse performance. Again, it's only a few percentage points, and if someone is gung-ho for THE on W2K, I won't stand in their way. Brian Brian Madden brian@xxxxxxxxxxxxxxx +1.202.302.3657 Sign up now for BriForum 2005: A 100% technical, 100% independent server-based computing conference from April 11-12, 2005. Visit www.briforum.com for details. -----Original Message----- From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf Of Bob Sent: Thursday, September 30, 2004 10:57 AM To: thin@xxxxxxxxxxxxx Subject: [THIN] Re: Hyperthreading Thanks, Jim... great article on the benefits of HTE -but- Intel is criminally terse in their statement that it should be disabled on Win2k. I can't tell if their rationale is functional or political. I'm about to rock the boat here, and I'm going to be asked tough questions. I'm hoping somebody will weigh in with some personal trials. Thanks, Bob ----- Original Message ----- From: Jim Kenzig http://thethin.net <jimkenz@xxxxxxxxxxxxxx> Date: Thu, 30 Sep 2004 07:06:52 -0700 (PDT) Subject: [THIN] Re: Hyperthreading To: thin@xxxxxxxxxxxxx See http://www.2cpu.com/articles/42_1.html http://thethin.net/faqs2.cfm?id=444&category=1&sortby=score Leave it off for Win2K! http://thethin.net/faqs2.cfm?id=443&category=1&sortby=score Regards, Jim Kenzig http://thin.net Bob <bobmails@xxxxxxxxx> wrote: Has anybody experimented with Hyperthreading On -vs- Off on Win2k servers? I've heard rumblings that it can be problematic, and perhaps decrease performance. I noticed that most SpecInt. winners have it disabled. I'm considering disabling it on one of my farm servers to observe the results. If anybody else has experimented I'd love to hear about it. Thanks in advance, Bob ******************************************************** This Weeks Sponsor RTO Software Do you know which applications are abusing your CPU and memory? 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