Debian latency test

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Debian latency test

danwe
Hello,

is there any program to test the intern latency of Debian? So I just need to know how much time the Linux Kernel needs to response to a request.

Kind regards

Daniel
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Re: Debian latency test

Roberto C. Sánchez-2
On Fri, Aug 16, 2019 at 02:31:38PM +0200, danwe wrote:
>    Hello,
>    is there any program to test the intern latency of Debian? So I just need
>    to know how much time the Linux Kernel needs to response to a request.
>    Kind regards
>    Daniel

You don't mention what sorts of requests, but two utilities that you may
find useful are iostat (in the sysstat package) and perf (in the
linux-perf package).

Regards,

-Roberto

--
Roberto C. Sánchez

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Re: Debian latency test

Reco
In reply to this post by danwe
        Hi.

On Fri, Aug 16, 2019 at 02:31:38PM +0200, danwe wrote:
> is there any program to test the intern latency of Debian? So I just need
> to know how much time the Linux Kernel needs to response to a request.

latencytop comes to mind first.
strace can be used for this, assuming that you know which syscall you
want to check.
bpftrace definitely can do it, but some learning is required.

Reco

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Re: Debian latency test

Henning Follmann
In reply to this post by danwe
On Fri, Aug 16, 2019 at 02:31:38PM +0200, danwe wrote:
> Hello,
>
> is there any program to test the intern latency of Debian? So I just need
> to know how much time the Linux Kernel needs to response to a request.
>
> Kind regards
>
> Daniel

This measurements will be meaningless unless you have a
real time enabled kernel. The kernel does not provide
predictable responsetimes without rt.


-H


--
Henning Follmann           | [hidden email]

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Re: Debian latency test

danwe
I do have Xenomai 2 with RTnet and Xenomai 3 without RTnet. I have tested "latency" on both to see how fast the Kernel can react to a request. In that context I do not want to measure how fast e.g. real-time udp frames will be. I just need to know how fast the Kernel could be.

Am Fr., 16. Aug. 2019 um 14:52 Uhr schrieb Henning Follmann <[hidden email]>:
On Fri, Aug 16, 2019 at 02:31:38PM +0200, danwe wrote:
> Hello,
>
> is there any program to test the intern latency of Debian? So I just need
> to know how much time the Linux Kernel needs to response to a request.
>
> Kind regards
>
> Daniel

This measurements will be meaningless unless you have a
real time enabled kernel. The kernel does not provide
predictable responsetimes without rt.


-H


--
Henning Follmann           | [hidden email]

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Re: Debian latency test

Étienne Mollier
In reply to this post by Reco
Reco, on 2019-08-16:
> On Fri, Aug 16, 2019 at 02:31:38PM +0200, danwe wrote:
> > is there any program to test the intern latency of Debian? So
> > I just need
> > to know how much time the Linux Kernel needs to response to a
> > request.
[...]
> bpftrace definitely can do it, but some learning is required.

Yes, I confirm that is a great tool!

The following page is a nice kick starter to begin to proceed to
measures and various data acquisition, teaching by example:

        https://github.com/iovisor/bpftrace/blob/master/docs/tutorial_one_liners.md

Just be careful with the injection of code at trace points or
kprobes: the more you inject code for your measure, the more the
targeted kernel operation will take time, thus slowing the
machine et providing you with underestimated results.

Have fun,  :)
--
Étienne Mollier <[hidden email]>
              5ab1 4edf 63bb ccff 8b54  2fa9 59da 56fe fff3 882d



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