Re: 2.6.19-rc1: Volanomark slowdown

On Wed, 8 Nov 2006 23:10:28 +0100
Olaf Kirch [off-list ref] wrote:

On Wed, Nov 08, 2006 at 10:38:52AM -0800, Tim Chen wrote:

quoted

The patch in question affects purely TCP and not the scheduler.  I don't

I know.

quoted

think the scheduler has anything to do with the slowdown seen after
the patch is applied.

In fixing performance issues, the most obvious explanation isn't always
the right one. It's quite possible you're right, sure.

What I'm saying though is that it doesn't rhyme with what I've seen of
Volanomark - we ran 2.6.16 on a 4p Intel box for instance and it didn't
come close to saturating a Gigabit pipe before it maxed out on CPU load.

quoted

The total number of messages being exchanged around the chatrooms in 
Volanomark remain unchanged.  But ACKS increase by 3.5 times and
segments received increase by 38% from netstat.  

quoted

So I think it is reasonable to conclude that the increase in TCP traffic
reduce the bandwidth and throughput in Volanomark.

You could count the number of outbound packets dropped on the server.

Olaf

Also under benchmark stress, the load can get so high that timers go
off that normally don't. For example, I have seen delayed ack timer
cause extra ack's when at lower loads the response happened quick enough
that the ACK was piggybacked.


-- 
Stephen Hemminger [off-list ref]