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Network transmit queue limitsNetwork transmit queue limitsPosted Aug 12, 2011 12:09 UTC (Fri) by ajb (subscriber, #9694)Parent article: Network transmit queue limits
I wonder if it wouldn't work better to define the queue length in microseconds, rather than bytes. That seems to be what this mechanism is approximating.
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Network transmit queue limits Posted Aug 12, 2011 16:55 UTC (Fri) by dlang (✭ supporter ✭, #313) [Link]
time is _much_ harder to estimate and measure than bytes.
if you have a full-duplex connection (i.e. hard-wired ethernet on modern switches), bytes and time have a very close correlation.
if you are on a shared media connection (unfortunantly including all radio based systems), then the correlation is not as close due to the fact that you can't know ahead of time how long it will take to send the data (you have to wait for other systems, retry, etc)
I think bytes is as accurate as you are going to be able to get.
Network transmit queue limits Posted Aug 12, 2011 17:25 UTC (Fri) by ajb (subscriber, #9694) [Link] I was thinking of something along the lines of:
void q_add(Q *q,PKT *pkt)
{
// timestamp packet
pkt->time=now();
// add packet to end of list
*q->last=pkt;
q->last=&pkt->next;
}
PKT *q_get(Q *q)
{
PKT *pkt=q->first;
if((pkt->time+q->max_time) < now())
{
free(pkt);
return 0;
}
else
{
return pkt;
}
}
No estimation at all. There are weaknesses in this approach, but it's simpler than adjusting a byte length.
Network transmit queue limits Posted Aug 13, 2011 7:40 UTC (Sat) by butlerm (subscriber, #13312) [Link]
Getting the time accurate to microseconds can be a rather expensive operation, unfortunately, and that weighs against regulating queue lengths in terms of time when a simple proxy like bytes is available.
Network transmit queue limits Posted Aug 24, 2011 15:03 UTC (Wed) by wtanksleyjr (guest, #74601) [Link]
It seems to me -- ignorance alert! -- that the problem isn't the bytes or the time at all; it's the variance. The purpose of a queue isn't to make a device send faster or slower; it's to cover up variance.
The sources of the variance will have to be considered carefully; variance caused by time delays on the output is probably different from that caused by multiple clients asynchronously loading data into the input.
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