# Misc questions, regarding Interrupt coalescing

**URL:** <https://www.ruby-forum.com/t/misc-questions-regarding-interrupt-coalescing/237050>\
**Category:** GNU Radio\
**Created:** [October 21, 2013, 10:20pm UTC](https://www.ruby-forum.com/t/misc-questions-regarding-interrupt-coalescing/237050 "2013-10-21T22:20:39Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![alcina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a587f6/32.png) [@alcina](https://www.ruby-forum.com/u/alcina)\
**Post date:** [October 21, 2013, 10:20pm UTC](https://www.ruby-forum.com/t/misc-questions-regarding-interrupt-coalescing/237050/1 "2013-10-21T22:20:39Z")

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Hello GR Forum,

I got some questions:

1/ Did anyone already tested the effect of Interrupt coalescing on  
reducing  
the latency when host and USRP N2X0 are communicating and how far did he  
reduce this latency

2/ I want to check first if my NIC got this feature enabled ?  
How do I have to proceed to check then how to test ?

3/ When running a stream of packets over the USRP I got the following  
error:

thread[thread-per-block[24]: \<gr\_block message\_source (8)\>]: msg length  
is  
not a multiple of d\_itemsize  
This error is raised after a fixed number N of successfully sent packets  
Could you please give me some hints on this issue.

Best regards,

–  
View this message in context:  
[http://gnuradio.4.n7.nabble.com/Misc-questions-regarding-Interrupt-coalescing-tp44285.html](http://gnuradio.4.n7.nabble.com/Misc-questions-regarding-Interrupt-coalescing-tp44285.html)  
Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).

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**Author:** ![naeo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/57b2e6/32.png) [@naeo](https://www.ruby-forum.com/u/naeo)\
**Post date:** [October 22, 2013, 11:13am UTC](https://www.ruby-forum.com/t/misc-questions-regarding-interrupt-coalescing/237050/2 "2013-10-22T11:13:11Z")

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Hi Naceur,

while questions 1 and 2 definitely are more of material for usrp-users,  
I’ll try to answer them as briefly as possible, and puit usrp-users into  
the CC:.  
On 10/21/2013 10:19 PM, Naceur wrote:

> 1/ Did anyone already tested the effect of Interrupt coalescing on reducing  
> the latency when host and USRP N2X0 are communicating and how far did he  
> reduce this latency  
> I haven’t specifically tested that.  
> However, Interrupt Coalescing should not decrease latency; on the  
> contrary, it should increase raw network latency but reduce CPU load.  
> This could even lead to decreased overall latency, however, as long as  
> NIC interrupts do not happen faster than they can be processed (leading  
> to packet loss in the long run), it probably won’t.  
> 2/ I want to check first if my NIC got this feature enabled ?  
> How do I have to proceed to check then how to test ?  
> Good question. It’s not only that your NIC needs to support input  
> moderation, your OS needs to do that, too!  
> ethtool is your friend under recent GNU/linuxes, try ethtool  
> –show-coalesce . However, on my devices, that  
> always tells me that it cannot get device coalesce settings.  
> 3/ When running a stream of packets over the USRP I got the following error:
> 
> thread[thread-per-block[24]: \<gr\_block message\_source (8)\>]: msg length is  
> not a multiple of d\_itemsize  
> This error is raised after a fixed number N of successfully sent packets  
> Could you please give me some hints on this issue.  
> Hm could you give some more hints on this issue? The error has something  
> to do with a message source, and you talk about packets, but you don’t  
> say anything on the actual flowgraph you’re using.

Hope I was able to help you a bit,  
Marcus

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<div class="post-metadata">

**Author:** ![naeo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/57b2e6/32.png) [@naeo](https://www.ruby-forum.com/u/naeo)\
**Post date:** [October 23, 2013, 11:39pm UTC](https://www.ruby-forum.com/t/misc-questions-regarding-interrupt-coalescing/237050/3 "2013-10-23T23:39:54Z")

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Unfortunately last nights mail didn’t get to the mailing list. But here  
it is.

Hi,

first of all you might be interested in [1]. Depending on the actual  
setup of your NIC latency depends a lot on interrupt coalescing. There  
is also some further reading on this page.

Have fun

[1] [http://code.ettus.com/redmine/ettus/projects/public/wiki/Latency](http://code.ettus.com/redmine/ettus/projects/public/wiki/Latency)