[THIN] Re: Hyperthreading

  • From: Bob <bobmails@xxxxxxxxx>
  • To: thin@xxxxxxxxxxxxx
  • Date: Thu, 30 Sep 2004 12:53:17 -0400

Thanks, Bernd.  I am trying to get TScale approved for testing as we speak!

I have noticed odd affinities during running processes.  Occasionally,
we'll have an instance of an application that will set one "threads"
floor at 30-40% proc. usage.  The other 3 threads operate normally.  
For instance... thread 0, 2, and 3 will be at 37% proc. usage, while
thread 1 is at 67%.  It hasn't caused a problem, per se, but it does
throw off the CPU numbers in perfmon and for one of my load evaluator
rules.

Kind Regards,
Bob


On Thu, 30 Sep 2004 12:18:07 -0400, Bernd Harzog
<bernd.harzog@xxxxxxxxxxx> wrote:
> 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
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> 
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