Updates using idle bandwidth
Les Mikesell
lesmikesell at gmail.com
Wed Mar 26 16:29:10 UTC 2008
Sunil Ghai wrote:
>
> >> A good question then is how do you set congestion level off and
> not get the
> >> kernel module loaded (if its not needed you wouldn't want it
> loading just to
> >> have it do nothing). Does setting TCP_CONGESTION = 0 result in
> not loading the
> >> module or does it just not limit traffic?
>
> Yes, yum is mostly receiving. An application can control receive
> bandwidth simply by rate-limiting its reads from the socket, but it will
> have no idea what an appropriate rate might be.
>
>
> Won't this *dynamic* rate-limiting be decided by TCP-LP congestion
> control mechanism to use only idle bandwidth? And could someone tell me
> what problems I might face if I make it to work with yum?
>
> PS: I am really new to this, please forgive me if any question asked
> doesn't make sense. :)
I don't understand what it does well enough to be sure, but normally
sending and receiving packets are completely independent events and a
receiver doesn't know whether a packet traversed congested links or not.
If you are actually dropping packets (which should only happen under
horrible conditions anyway), a congestion-aware receiver should send a
duplicate ack for the previous correct packet and the sender may use
this as an indication to back off. But when you are actually dropping
packets, it is way to late to be thinking about using only idle
bandwidth - you've already backed everything up past its buffer windows.
--
Les Mikesell
lesmikesell at gmail.com
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