[USRP-users] Underflows problem but limited CPU usage

Damien Serant damien.serant at gmail.com
Wed Dec 10 04:10:47 EST 2014

Many thanks for the quick response.
Which value do you suggest me for the recv_buff_size ? I read that the
default value was 50Mo, do you confirm ?
Is there an interest to change also with the recv_frame_size value ?



2014-12-10 1:20 GMT+01:00 Michael West <michael.west at ettus.com>:

> That sounds like an OS issue to me.  A few things to try:
> - Enable Receive Side Scaling (if not already enabled)
> - Increase the size of the receive socket buffer
> - Disable all power management (may be throttling CPU cores)
> - Use a single Ethernet connection (reduce the number of network
> interrupts)
> Hardware interrupts trump all software, so changing priority will not
> matter if there are more hardware interrupts to process than can be
> processed (i.e. from the NIC and mouse).  A good test is to see how much
> kernel activity there is on each core when shaking the console window and
> running UHD.  If there is a concentrated kernel load on a single core, that
> is a good indication that all interrupts are being handled by a single core
> and that is why packet processing is being delayed.  Enabling Receive Side
> Scaling will spread the network interrupts among the cores and increasing
> the socket buffer will give more time to process the interrupts.
> Regards,
> Michael E. West
> On Tue, Dec 9, 2014 at 2:59 PM, Damien Serant via USRP-users <
> usrp-users at lists.ettus.com> wrote:
>> Hi list,
>> I'm trying to push the USRPN200 to the limit in throughput and I
>> experienced a quite strange underflow behavior.
>> Here is my configuration :
>>    - 2USRPN200 with Mimo cable, 25MHz and 8 bit on each with 2 Ethernet
>>    to avoid saturation of the link
>>    - Intel Xeon processor with 6 core (12 Threads)
>>    - Windows 7 Pro 64 bit
>> My UHD program is only reading samples without any processing (not even
>> disk writing). If i do nothing else on the PC, the program work without any
>> packet loss with a very limited CPU charge of about 5% (about 20% on two
>> cores) according to the task manager and for at least 30 minutes (the
>> longest test that i made). As soon as i start soliciting a bit the CPU
>> (e.g. opening another application, or simply by moving the scroll bar of
>> the console up and down or shaking the console window) underflows and
>> packet losses arise. I tried to play with the process priority but the
>> result is the same.
>> The underflows are apparently due to an increased CPU charge but with
>> only 5% of CPU usage for my UHD program i should not expect that, no ?
>> Does anyone already experienced that ?
>> Is there some tricks in the OS configuration or in UHD configuration to
>> avoid that ?
>> Thanks in advance,
>> Damien
>> _______________________________________________
>> USRP-users mailing list
>> USRP-users at lists.ettus.com
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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