Re: Samba performance / zero-copy network I/O

[Gord R. Lamb]

On Wed, 14 Feb 2001, Tom Sightler wrote:

> Quoting "Gord R. Lamb" <[e-mail]>:
>
> > On Wed, 14 Feb 2001, Jeremy Jackson wrote:
> >
> > > "Gord R. Lamb" wrote:
> > > > in etherchannel bond, running
> > linux-2.4.1+smptimers+zero-copy+lowlatency)
>
> Not related to network, but why would you have lowlatency patches on
> this box?

Well, I figured it might reduce deadweight time between the different
operations (disk reads, cache operations, network I/O) at the expense of a
little throughput.  It was just a hunch and I don't fully understand the
internals (of any of this, really).  Since I wasn't saturating the disk or
network controller, I thought the gain from quicker response time (for
packet acknowledgement, etc.) would outweigh the loss of individual
throughputs.  Again, I could be misunderstanding this completely. :)

> My testing showed that the lowlatency patches abosolutely destroy a
> system thoughput under heavy disk IO.  Sure, the box stays nice and
> responsive, but something has to give.  On a file server I'll trade
> console responsivness for IO performance any day (might choose the
> opposite on my laptop).

Well, I backed out that particular patch, and it didn't seem to make much
of a difference either way.  I'll look at it in more detail tomorrow
though.

Cya.

> My testing wasn't very complete, but heavy dbench and multiple
> simultaneous file copies both showed significantly lower performance
> with lowlatency enabled, and returned to normal when disabled.
>
> Of course you may have had lowlatency disabled via sysctl but I was
> mainly curious if your results were different.
>
> Later,
> Tom
>