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Posted to jmeter-dev@jakarta.apache.org by Jordi Salvat i Alabart <js...@atg.com> on 2002/12/22 00:18:11 UTC
Time travel? Or vaticinating web server?
Hi.
While trying to test JMeter for measurement accuracy, I've discovered
the principle for time-travel. Or maybe it's my Apache web server, which
is capable of responding to requests before it receives them... I think
I'll request a patent for that and make my first million...
Seriously: I'm seeing negative times in my samples.
So, I've created the attached bit of code, which shows that
System.currentTimeMillis() is not reliable. I'm using Linux with a
2.4.18 kernel and libc6 2.3.1-5. The problem occurs with the following JDKs:
java version "1.3.1"
Java(TM) 2 Runtime Environment, Standard Edition (build
Blackdown-1.3.1-02b-FCS)Java HotSpot(TM) Client VM (build
Blackdown-1.3.1_02b-FCS, mixed mode)
java version "1.4.1_01"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_01-b01)
Java HotSpot(TM) Client VM (build 1.4.1_01-b01, mixed mode)
Can someone please try this on a different O.S., to see if it's my
system or the JDK?
Thanks,
Jordi.
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Re: Time travel? Or vaticinating web server?
Posted by Jordi Salvat i Alabart <js...@atg.com>.
Managed to get access to a Solaris box. The problem doesn't happen there
on any JDKs (I've tested 1.2.2, 1.3.1 and 1.4.0).
I've already filed a bug with Blackdown Java.
Meanwhile, you should probably take the accuracy of any results on Linux
with two grains of salt.
Salut,
Jordi.
Jordi Salvat i Alabart wrote:
> Hi.
>
> While trying to test JMeter for measurement accuracy, I've discovered
> the principle for time-travel. Or maybe it's my Apache web server, which
> is capable of responding to requests before it receives them... I think
> I'll request a patent for that and make my first million...
>
> Seriously: I'm seeing negative times in my samples.
>
> So, I've created the attached bit of code, which shows that
> System.currentTimeMillis() is not reliable. I'm using Linux with a
> 2.4.18 kernel and libc6 2.3.1-5. The problem occurs with the following
> JDKs:
>
> java version "1.3.1"
> Java(TM) 2 Runtime Environment, Standard Edition (build
> Blackdown-1.3.1-02b-FCS)Java HotSpot(TM) Client VM (build
> Blackdown-1.3.1_02b-FCS, mixed mode)
>
> java version "1.4.1_01"
> Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_01-b01)
> Java HotSpot(TM) Client VM (build 1.4.1_01-b01, mixed mode)
>
> Can someone please try this on a different O.S., to see if it's my
> system or the JDK?
>
> Thanks,
>
> Jordi.
>
>
>
>
> --
> To unsubscribe, e-mail:
> <ma...@jakarta.apache.org>
> For additional commands, e-mail:
> <ma...@jakarta.apache.org>
>
>
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Re: Time travel? Or vaticinating web server? - SOLUTION
Posted by Jordi Salvat i Alabart <js...@atg.com>.
I've finally solved this issue. Posting here for the benefit of list
lurkers and archive readers who may hit the same problem in the future:
This was actually a Linux Kernel "bug". I've fixed it by upgrading to a
2.4.20 kernel built with CONFIG_X86_TSC_DISABLE set. I don't know
whether there's a solution for earlier kernels (this config var doesn't
exist in 2.4.18).
From the 2.4.20 kernel Configure.help:
Unsynced TSC support
CONFIG_X86_TSC_DISABLE
This option is used for getting Linux to run on a NUMA multi-node
boxes, laptops and other systems suffering from unsynced TSCs or
TSC drift, which can cause gettimeofday to return non-monotonic values.
Choosing this option will disable the CONFIG_X86_TSC optimization,
and allows you to then specify "notsc" as a boot option regardless of
which processor you have compiled for.
NOTE: If your system hangs when init should run, you are probably
using a i686 compiled glibc which reads the TSC without checking for
availability. Boot without "notsc" and install a i386 compiled glibc
to solve the problem.
If unsure, say N.
Salut,
Jordi.
Jordi Salvat i Alabart wrote:
> Hi.
>
> While trying to test JMeter for measurement accuracy, I've discovered
> the principle for time-travel. Or maybe it's my Apache web server, which
> is capable of responding to requests before it receives them... I think
> I'll request a patent for that and make my first million...
>
> Seriously: I'm seeing negative times in my samples.
>
> So, I've created the attached bit of code, which shows that
> System.currentTimeMillis() is not reliable. I'm using Linux with a
> 2.4.18 kernel and libc6 2.3.1-5. The problem occurs with the following
> JDKs:
>
> java version "1.3.1"
> Java(TM) 2 Runtime Environment, Standard Edition (build
> Blackdown-1.3.1-02b-FCS)Java HotSpot(TM) Client VM (build
> Blackdown-1.3.1_02b-FCS, mixed mode)
>
> java version "1.4.1_01"
> Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_01-b01)
> Java HotSpot(TM) Client VM (build 1.4.1_01-b01, mixed mode)
>
> Can someone please try this on a different O.S., to see if it's my
> system or the JDK?
>
> Thanks,
>
> Jordi.
>
>
>
>
> --
> To unsubscribe, e-mail:
> <ma...@jakarta.apache.org>
> For additional commands, e-mail:
> <ma...@jakarta.apache.org>
>
>
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Re: AW: Time travel? Or vaticinating web server?
Posted by Jordi Salvat i Alabart <js...@atg.com>.
Oops. Here it goes.
Wolfram Rittmeyer wrote:
> Hi Jordi,
>
> I'd like to test it this evening on my Linux-Box running Suns jdk1.4. Would
> be nice if you could send the attachment, mentioned in your mail, since it
> seems not to be attached yet ;-)
>
> Greetings,
>
> Wolfram
>
>
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>
>
AW: Time travel? Or vaticinating web server?
Posted by Wolfram Rittmeyer <w....@proplant.de>.
Hi Jordi,
I'd like to test it this evening on my Linux-Box running Suns jdk1.4. Would
be nice if you could send the attachment, mentioned in your mail, since it
seems not to be attached yet ;-)
Greetings,
Wolfram
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