Re: Poor PostgreSQL scaling on Linux 2.6.25-rc5 (vs 2.6.22)

Willy Tarreau
2008-03-17T05:24:16Z

On Sun, Mar 16, 2008 at 10:16:36PM -0700, Ray Lee wrote:
> On Sun, Mar 16, 2008 at 5:44 PM, Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> > I don't see how it is really helpful for interactive processes either.
> > By definition, if they are not CPU bound, then they should be run
> > quite soon after waking up; if they are CPU bound, then reducing
> > efficiency by increasing context switches is effectively going to
> > increase their latency anyway.
>
> How? Are you saying that switching the granularity to, say, 25ms, will
> *decrease* the latency of interactive tasks?
>
> And the efficiency we're talking about reducing here is due to the
> fact that tasks are hitting cold caches more times per second when the
> granularity is smaller, correct? Or are you concerned by another
> issue?
>
> > Can this be changed by default, please?
>
> Not without benchmarks of interactivity, please. There are far, far
> more linux desktops than there are servers. People expect to have to
> tune servers (I do, for the servers I maintain). People don't expect
> to have to tune a desktop to make it run well.

Oh and even on servers, when your anti-virus proxy reaches a load of 800,
you're happy no to have too large a time-slice so that you regularly get
a chance of being allowed to type in commands over SSH.

Large time-slices are needed only in HPC environments IMHO, where only
one task runs.

Willy

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