|To:||Stephen Hemminger <shemminger@xxxxxxxx>|
|Subject:||Re: [PATCH] Too aggressive cwnd backoff|
|From:||Baruch Even <baruch@xxxxxxxxx>|
|Date:||Thu, 07 Apr 2005 19:14:45 +0100|
|Cc:||"David S. Miller" <davem@xxxxxxxxxxxxx>, netdev@xxxxxxxxxxx, Werner Almesberger <werner@xxxxxxxxxxxxxxx>|
|User-agent:||Debian Thunderbird 1.0 (X11/20050116)|
Stephen Hemminger wrote:
On Thu, 7 Apr 2005 19:41:46 +0300 Baruch Even <baruch@xxxxxxxxx> wrote:The provided patch will set limit to tp->ssthresh. This was the original behaviour in some older version of Linux.I think this is a real problem, and was observed by Werner with umlsim. Don't know when it got introduced because it appears to pre-date the '04 work in adding Westwood, BIC, Vegas. Perhaps Alexey can shed some light on this. Going back to the pre-westwood code in BK, the /2 is still there.
This wasn't there in 2.4.23 on which on the original work of H-TCP was done. I've encountered it in my work on the 2.6.6 version, but didn't understand all the implications at the time. I've re-encountered it now that I'm redoing the patches to 2.6.11, and it's as good a time as ever to resolve it.
The effect is not catastrophic, but it does mean that we leave recovery into slow-start like ascend of cwnd until we get to ssthresh again. It does mean that after recovery we inject a lot of packets to the network at a very fast rate.
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