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Re: [Discuss-gnuradio] Debugging overruns

From: Dan Halperin
Subject: Re: [Discuss-gnuradio] Debugging overruns
Date: Sat, 27 Jan 2007 16:25:19 -0800
User-agent: Thunderbird (X11/20070103)

Eric Blossom wrote:
> overruns or underruns?

uO means a USRP Overrun right?

> Underruns are to be expected with tunnel.py, assuming that you're not
> feeding it data constantly.
> (When the in-band signaling stuff is complete, we'll have a more
> sensible interpretation for the underrun case.  It'll only
> report a problem if it occurs within a packet, not between packets.)
> Are you running with real time scheduling enabled?  If you run
> tunnel.py as root (or having CAP_SYS_NICE) it'll be enabled (currently
> only implemented on system that implement sched_setscheduler.)

Real-time scheduling is enabled. The process gets priority -50. Also,
another (incidental) question, I get really bad performance when the
fusb_options set by realtime being true are used....

> Have you enabled logging? Turn it off.

Logging is off.

> Linux or some other OS?

Ubuntu 6.10 (but installed before all the recent libtool fun).

> Does the unmodified tunnel.py exhibit the same behavior?
> Does benchmark_tx.py / benchmark_rx.py work without over/underruns?

No, yes.

I suspect the problem is something to do with randomization; I'm trying
to write a more comprehensive benchmark where I send random payloads.
Using 1024 byte packets (i.e. 1024 random bytes generated per packet), I
can get 524+/- 1 sent. With 768-byte packets, I can send 700+/-1. With
1200-byte packets, I can send 445 packets, more or less. The product of
all of these numbers is close;

>>> 1200*445
>>> 1024*524
>>> 768*700

Perhaps python does something funky after a certain number of bytes? I'm
using these functions:

from random import seed,randint

def rand_init(s=0):

def random_bytes(number):
    ret = ""
    for i in range(number):
        ret += chr(randint(0, 255))
    return ret

Or could it be some garbage collection kicking in? I know that this
function is extraordinarily wasteful of memory... Except then it doesn't
make sense as to why that product would be constant..


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