Is a client robot an OS thread?

[Pavel Kazlenka]

Hi Alberto,

On 09/09/2013 04:40 AM, Alberto Klocker wrote:
> Hi,
> We run tests on a 10 Gb network environment with Polygraph as one of the benchmarking tools but have found we are hitting 100% CPU usage on both the poly-client and poly-server which would indicate we need to spread the processes and systems out.
> How well does the reporting engine handle log files from multiple sources?
> Say I were to script a system that launches two or three instances of the client and server, will the reporting engine be capable of combining the results into one report?
All the polygraph reporting tools (like polygraph-lx, polygraph-ltrace, 
polygraph-reporter) support multiple logs aggregation. E.g. if you have 
logs from three client workers named clt.1.log, clt.2.log, clt.3.log you 
can extract statistics from them simply using
$ polygraph-lx clt.1.log clt.2.log clt.3.log. Same for others. However, 
there is a minor bug that prevents from ltrace tool extracting logs from 
both server and client sides in one run: 
https://bugs.launchpad.net/polygraph/+bug/1204983
> Would it be better I write something that "merges" the results together?
As a result of written above, you don't have to write anything.
> I'm curious to see what others have done to ramp Polygraph up above its single core limits.
> We can get 10 Gb throughput with large files but my goal is to find maximum, stable concurrent connections.
> Any help is much appreciated!
Sure Alberto. There is a number of actions that could help you increase 
polygraph performance:

1) Run multiple instances of workers and bind them to different cpu 
cores. E.g if you have 2 cpu cores on machine that runs 
polygraph-client, run two clients like:
taskset -c 0 polygraph-client --log clt.1.log ...
taskset -c 1 polygraph-client --log clt.2.log ...

2) Bind tune cpu affinity for NIC interrupts to cores different from the 
ones that already occupied by polygraph workers (clients or servers). 
E.g. if you have 4 cpu cores, consider to run three polygraph-client 
instances bound to cores 0-2 and bind NIC interrupts to core 3. This 
article should help you with SMP affinity in linux: 
http://www.alexonlinux.com/smp-affinity-and-proper-interrupt-handling-in-linux 
. There is no good formula to say what should be ratio between workers' 
and NIC's cores, but top output could give you the clues.

3) If you have 'virtual' (hyper-threading provided) cores, it's not a 
good idea to bind polygraph workers to both 'real' and 'virtual' 
instances of the same core.

4) If you have enough RAM, consider writing  test results on in-memory 
FS like tmpfs 
(https://www.kernel.org/doc/Documentation/filesystems/tmpfs.txt).

5) Tuning linux TCP stack for 10G networking is important part too. I'd 
use this document as a guide: 
http://landley.net/kdocs/ols/2009/ols2009-pages-169-184.pdf .

Best wishes,
Pavel
>
> Kevin Xie1 <Kevin_Xie1 at symantec.com  <http://www.web-polygraph.org/mailman/listinfo/users>> writes:
>
> >/  Thanks for your quick response, Dmitry.
> />/
> />/  However, I don't understand how a single thread can simulate multiple
> />/  concurrent "users" submitting request to web servers. Is it that the
> />/  single thread iterates all open connections one by one (submitting a
> />/  request or processing response one at a time)?
> /
> Sort of, though details are more complex than that.  If you are
> interested, search for I/O multiplexing.
>
> >/  bound by CPU since just 1 core is used at a time, or by slow
> />/  connections ..., do I miss something here, or my understanding is
> />/  fundamentally wrong?
> />/
> /
> The fact that a single polygraph process can use only a single core may
> be a limitation indeed.  But moving each simulated agent to a separate
> OS thread is not the solution.
>
> You can run multiple Polygraph client or server processes on a single
> system.  But that makes it harder to manage the test and usually
> requires some auxiliary scripts to start all processes.
>
> It would be nice to have SMP support in Polygraph and we have some ideas
> about it.  But so far there has not been enough interest in such
> project.  Patches or sponsorships are welcome.
>
> In any case, please do not make conclusions about Polygraph performance
> from the fact that it is single-threaded.  Polygraph is successfully
> used for high performance tests in 10Gbit networks (though it may
> require multiple Polygraph processes and/or systems).
>
> Regards,
>    Dmitry
>
> >/  Appreciated for any light shed!
> />/
> />/  Kevin
> />/
> />/  -----Original Message-----
> />/  From: Dmitry Kurochkin [mailto:dmitry.kurochkin at measurement-factory.com  <http://www.web-polygraph.org/mailman/listinfo/users>]
> />/  Sent: May-03-12 3:19 PM
> />/  To: Kevin Xie1
> />/  Cc:users at web-polygraph.org  <http://www.web-polygraph.org/mailman/listinfo/users>
> />/  Subject: Re: Is a client robot an OS thread?
> />/
> />/  Hi Kevin.
> />/
> />/  Kevin Xie1 <Kevin_Xie1 at symantec.com  <http://www.web-polygraph.org/mailman/listinfo/users>> writes:
> />/
> />>/  Hi,
> />>/
> />>/  Is a client robot a real OS thread? I'm using web polygrah in Linux,
> />>/  but I doesn't see multiple threads in the OS during a test with 500
> />>/  robots.
> />>/
> />/
> />/  Polygraph client and server processes are single-threaded.  All Robot
> />/  and Server agents are running in a single thread.
> />/
> />/  Regards,
> />/    Dmitry
> />/
> />>/  Thanks,
> />>/  Kevin/
> *Alberto Klocker* | Software Developer | www.bluereef.com.au 
> <http://www.bluereef.com.au/>
> ___________________________________________________________________
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