Jonathan Lynch wrote:
I dont understand what you mean when you say "if you could sample truly
randomly you would get a proper distribution".
Also having the timers synchronized will allow for more accurate
measurements of the delay. I cant see how this would have an impact on
the pattern.
I mean it's possibly just to do with the test if a 0ms - 1ms delay is
expected then you could see patterns arising depending on how you
measure delay/clock drift or something.
Now I have two pings that do intervels < 1 sec - the inetutils GNU ping
guys implemented it for me :-), and I also have the iputils one I can
simulate a stream better.
While doing this I noticed that iputils ping actually gives lower
latency readings when sending many pps. Using tcpdump deltas I can see
the network latency is the same however many pps I do - it's just that
when measuring <1ms delays and doing many pps it seems that some code
gets cached (guess) and the reported delay changes as a result.
I mention that just to illustrate that measuring small delays can be
misleading and influenced by the exact nature of your setup.
I have the default setting which is to set it to jiffies. There is a
comment in the kernal config for Packet scheduler clock source that
mentions that Jiffies "its resolution is too low for accurate shaping
except at very low speed". I will recompile the kernel and try the CPU
option tomorrow to see if there is any change.
Maybe not in the case of htb - I use CPU and see similar results, the
comment about accurate shaping was probably written when HZ=100, but I
suppose it will be better for something :-)
I didnt realise such options existed for htb (mpu + overhead). These parameters are not mentioned in the man pages or in the htb manual.
I presume I have to patch tc to get these features ?.
There is mention on the htb page - it was added as a patch so was not
designed in, which explains why burst doesn't use it.
You don't need to patch recent iproute2 it's already in there.
Andy.
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