Re: [Discuss-gnuradio] Misc questions, regarding Interrupt coalescing

[Marcus Müller]

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 
<ethernet device name>. 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