From patchwork Tue May 29 19:42:51 2012
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Subject: Low latency kernel for Quantal
Date: Tue, 29 May 2012 09:42:51 -0000
From: Tim Gardner <tim.gardner@canonical.com>
X-Patchwork-Id: 161792
Message-Id: <4FC526BB.6080100@canonical.com>
To: Leann Ogasawara <leann@canonical.com>
Cc: kernel-team <kernel-team@lists.ubuntu.com>

On 05/29/2012 10:13 AM, 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?
>
> rtg

And here is a pull request guaranteed to make your builds take longer.

The only clash that I see in the Quantal archive is with the lowlatency 
meta package. I'll have to add some 'Conflicts:' or 'Replaces:' in the 
mainline kernel meta package. Maybe I can get it removed completely 
since it was auto-synced.

rtg