Thread (40 messages) 40 messages, 10 authors, 2006-09-22

Re: high latency with TCP connections

From: Rick Jones <hidden>
Date: 2006-08-31 19:40:50

Kelly Burkhart wrote:
On 8/30/06, David Miller [off-list ref] wrote:
quoted
From: Stephen Hemminger <redacted>
quoted
Expecting any performance with one byte write's is silly.
This is absolutely true.  TCP_NODELAY can only save you when you are
sending a small amount of data "in aggregate", such as in an SSH or
telnet session, whereas in the case being shown here a large amount of
data is being sent in small chunks which will always get bad
performance.


The word performance in this list seems to always mean 'throughput'.
It seems though that there could be some knob to tweak for those of us
who don't care so much about throughput but care a great deal about
latency.
IIRC Apart from interactions with Nagle (TCP_NODELAY) or the mixing of 
packet and byte-based congestion control and avoidance heuristics, there 
really isn't much of anything else to tweak in TCP.  If it can send 
data, it sends data.

Where there _is_ a knob to turn these days might be down with the 
drivers and their NICs' use of interrupt coalescing:

ftp://ftp.cup.hp.com/dist/networking/briefs/nic_latency_vs_tput.txt

rick jones
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