Low latency kernel for Quantal

[Andy Whitcroft]

On Tue, May 29, 2012 at 10:13:09AM -0600, Tim Gardner wrote:
> At UDS I committed to adding a low latency flavour to Quantal if we
> could collapse generic and virtual. It appears that we've been able to
> do so.
> 
> After looking at the lowlatency kernel in Precise
> (git://kernel.ubuntu.com/themuso/ubuntu-precise-lowlatency.git) it looks
> like the required config changes are:
> 
> CONFIG_HZ=1000
> CONFIG_NO_HZ=n
> CONFIG_PREEMPT=y
> CONFIG_PREEMPT_RCU=y
> 
> and some other config options that get enabled as a result of the above
> changes.
> 
> The only relevant code patch is 'UBUNTU: SAUCE: Made kernel irq-threaded
> by default' which changes the default behavior of forced IRQ threads to
> enabled, and adds a kernel boot parameter to override the default. I
> propose that we _not_ carry this patch in Quantal if the lowlatency
> installer can add 'threadirqs' to the grub kernel command line.
> 
> Thoughts?

If we have a patch then the logical thing to do is make it add a new
configuration option for the default for this so the config can carry
the difference correctly.

-apw