Re: Although CONFIG_IRQBALANCE is enabled IRQ's don't seem to be balanced very well

[Nauman Tahir <nauman.tahir@gmail.com>]

On 1/10/06, Jesper Juhl <jesper.juhl@gmail.com> wrote:
> On 1/10/06, Martin Bligh <mbligh@mbligh.org> wrote:
> > Jesper Juhl wrote:
> > > On 1/10/06, Martin Bligh <mbligh@mbligh.org> wrote:
> > >
> > >>Josef Sipek wrote:
> > >>
> > >>>On Tue, Jan 10, 2006 at 12:14:42PM +0100, Jesper Juhl wrote:
> > >>>
> > >>>
> > >>>>Do I need any userspace tools in addition to CONFIG_IRQBALANCE?
> > >>>
> > >>>
> > >>>Last I checked, yes you do need "irqbalance" (at least that's what
> > >>>the package is called in debian.
> > >>
> > >>Nope - you need the kernel option turned on OR the userspace daemon,
> > >>not both.
> > >>
> > >
> > > Ok, good to know.
> > >
> > >
> > >>If you're not generating interrupts at a high enough rate, it won't
> > >>rotate. That's deliberate.
> > >>

What I have read is that first CPU is used more for interrupts to use
the concept of maximizing cache locality. Probably kernel is
optimizing this even with CONFIG option enabled.

Nauman

> > >
> > >
> > > Hmm, and what would count as "a high enough rate"?
> > >
> > > I just did a small test with thousands of  ping -f's through my NIC
> > > while at the same time giving the disk a good workout with tons of
> > > find's, sync's & updatedb's - that sure did drive up the number of
> > > interrupts and my load average went sky high (amazingly the box was
> > > still fairly responsive):
> > >
> > > root@dragon:/home/juhl# uptime
> > >  22:59:58 up 12:43,  1 user,  load average: 1015.48, 715.93, 429.07
> > >
> > > but, not a single interrupt was handled by CPU1, they all went to CPU0.
> > >
> > > Do you have a good way to drive up the nr of interrupts above the
> > > treshhold for balancing?
> >
> > Is it HT? ISTR it was intelligent enough to ignore that. But you'd
> > have to look at the code to be sure.
> >
> Dual Core Athlon 64 X2 4400+
>
> --
> Jesper Juhl <jesper.juhl@gmail.com>
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