[THIN] Re: Hyperthreading
- From: "Bernd Harzog" <Bernd.Harzog@xxxxxxxxxxx>
- To: <thin@xxxxxxxxxxxxx>
- Date: Thu, 30 Sep 2004 12:18:07 -0400
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
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-----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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