Start irqbalance by default

[Soren Hansen]

On Mon, Jan 11, 2010 at 11:14:20AM +0100, Martin Pitt wrote:
> Hello all,
> 
> Steve Langasek [2010-01-08 20:14 -0800]:
> >  Description: Daemon to balance interrupts for SMP systems
> >   Daemon to balance interrupts across multiple CPUs, which can lead to
> >   better performance and IO balance on SMP systems. This package is
> >   especially useful on systems with multi-core processors, as interrupts
> >   will typically only be serviced by the first core.
> 
> To be honest, this sounds a bit like black voodoo to me. How can it be
> more efficient to schedule interrupts in an userspace daemon than in
> the kernel itself (where it is already done presumably)?

   http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=8b8e8c1bf7275eca859fe551dfa484134eaf013b

> Does userspace have more information about which processes are running
> and what they are going to do? If so, doesn't that involve more IPC
> and thus wakeups?

irqbalance detects your CPU topology at startup (and at 5 minute
intervals in case something was hotplugged). It then occasionally looks
at the amount of interrupts generated by various devices (looking at
e.g.  /proc/interrupts) and based on this (and the type of device from
whence the interrupts originated), it assigns the device to a specific
cpu. It seems to be commonly believed that this is achieved much more
elegantly and cleanly in userspace than can (currently) be done
in-kernel.

-- 
Soren Hansen                 | 
Lead virtualisation engineer | Ubuntu Server Team
Canonical Ltd.               | http://www.ubuntu.com/
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