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Old 05-29-2012, 04:13 PM
Tim Gardner
 
Default Low latency kernel for Quantal

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
--
Tim Gardner tim.gardner@canonical.com

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Old 05-29-2012, 07:42 PM
Tim Gardner
 
Default Low latency kernel for Quantal

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
--
Tim Gardner tim.gardner@canonical.com
The following changes since commit e9849ef084905c4d764a8412b67723b3d6bb0619:

UBUNTU: Start new release (2012-05-29 06:32:22 -0700)

are available in the git repository at:

git://kernel.ubuntu.com/rtg/ubuntu-quantal.git lowlatency

for you to fetch changes up to 384a55ce2d109c71b19078685156751601868249:

UBUNTU: Added lowlatency flavour [i386 amd64] (2012-05-29 13:30:33 -0600)

----------------------------------------------------------------
Tim Gardner (1):
UBUNTU: Added lowlatency flavour [i386 amd64]

debian.master/abi/3.4.0-3.8/amd64/ignore.modules | 1 +
debian.master/abi/3.4.0-3.8/amd64/lowlatency |13013 ++++++++++++++++++++
.../abi/3.4.0-3.8/amd64/lowlatency.ignore | 1 +
debian.master/abi/3.4.0-3.8/i386/ignore.modules | 1 +
debian.master/abi/3.4.0-3.8/i386/lowlatency |13013 ++++++++++++++++++++
debian.master/abi/3.4.0-3.8/i386/lowlatency.ignore | 1 +
debian.master/config/amd64/config.common.amd64 | 1 -
debian.master/config/amd64/config.flavour.generic | 12 +
.../config/amd64/config.flavour.lowlatency | 15 +
debian.master/config/armel/config.common.armel | 9 +
debian.master/config/armhf/config.common.armhf | 9 +
debian.master/config/config.common.ubuntu | 19 +-
debian.master/config/i386/config.common.i386 | 1 -
debian.master/config/i386/config.flavour.generic | 12 +
.../config/i386/config.flavour.lowlatency | 15 +
debian.master/config/powerpc/config.common.powerpc | 11 +
debian.master/config/ppc64/config.common.ppc64 | 11 +
debian.master/control.d/vars.lowlatency | 6 +
debian.master/d-i/kernel-versions.in | 2 +
debian.master/rules.d/amd64.mk | 2 +-
debian.master/rules.d/i386.mk | 2 +-
21 files changed, 26142 insertions(+), 15 deletions(-)
create mode 100644 debian.master/abi/3.4.0-3.8/amd64/ignore.modules
create mode 100644 debian.master/abi/3.4.0-3.8/amd64/lowlatency
create mode 100644 debian.master/abi/3.4.0-3.8/amd64/lowlatency.ignore
create mode 100644 debian.master/abi/3.4.0-3.8/i386/ignore.modules
create mode 100644 debian.master/abi/3.4.0-3.8/i386/lowlatency
create mode 100644 debian.master/abi/3.4.0-3.8/i386/lowlatency.ignore
create mode 100644 debian.master/config/amd64/config.flavour.lowlatency
create mode 100644 debian.master/config/i386/config.flavour.lowlatency
create mode 100644 debian.master/control.d/vars.lowlatency
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Old 05-29-2012, 09:14 PM
Leann Ogasawara
 
Default Low latency kernel for Quantal

On 05/29/2012 12:42 PM, Tim Gardner wrote:

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.


Having just done some spring cleaning on our list of supported kernel
flavors, I'm a bit hesitant to just turn around now and throw some more
back on the list. Scott, can you refresh my memory what the convincing
argument was for why we want to add the low latency kernel flavor back
to list of flavors being maintained?



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.


Regardless of where this is maintained, this sounds reasonable
especially if it eliminates the need of carrying SAUCE patches.



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



The pull request looks to do what it claims. Although as I mentioned
above I'd like to hear the arguments for why we want this back on our
list of supported kernel flavors before I'll give my official Ack.


Thanks,
Leann

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Old 05-29-2012, 09:44 PM
Scott Lavender
 
Default Low latency kernel for Quantal

On Tue, May 29, 2012 at 4:14 PM, Leann Ogasawara <leann.ogasawara@canonical.com> wrote:



Having just done some spring cleaning on our list of supported kernel flavors, I'm a bit hesitant to just turn around now and throw some more back on the list. *Scott, can you refresh my memory what the convincing argument was for why we want to add the low latency kernel flavor back to list of flavors being maintained?





Thanks,

Leann


Hi Leann,
Currently the studio team has to manually update the -lowlatency kernel for each update. It was suggested that this could be rolled into a build config making the process much more streamlined and automated.

I believe there was also some discussion regarding*maintenance/support. I seem to recall the outcome was that the kernel team would *not* be responsible to support this kernel; although I admit I do not remember who determined this or if it was a consensus.

Please let me know if I can assist in any other way.
Thank you,ScottL
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Old 05-30-2012, 12:34 PM
Andy Whitcroft
 
Default Low latency kernel for Quantal

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

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