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    SubjectRe: 2.6.19-rc1: Volanomark slowdown
    On Wed, 8 Nov 2006 23:10:28 +0100
    Olaf Kirch <okir@suse.de> wrote:

    > On Wed, Nov 08, 2006 at 10:38:52AM -0800, Tim Chen wrote:
    > > The patch in question affects purely TCP and not the scheduler. I don't
    >
    > I know.
    >
    > > 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.
    >
    > > 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.
    >
    > > 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 <shemminger@osdl.org>
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