Re: [PATCH 2/7] ppc64el: kernel: config: little-endian powerpc64 options
On 05/28/2014 10:09 PM, Ben Hutchings wrote:
On Wed, 2014-05-28 at 20:29 -0300, Mauricio Faria de Oliveira wrote:
[...]
Also most architectures now use several types of NO_HZ, so the main
frequency is not really important anymore.
With that, I disagree.
The application of NO_HZ is only idle CPUs (given it's description,
tickless /idle/, and the rename to NO_HZ_IDLE with the introduction of
NO_HZ_FULL):
"""
CONFIG_NO_HZ_IDLE: [formerly CONFIG_NO_HZ=y], this turns off the
periodic tick when a CPU enters idle mode. [4]
"""
The target scenario for the systems running ppc64el is under-load,
not that idle. There, the lower interrupt rate helps.
The target scenario - for all systems with these processors? I thought
the point of OpenPower was to allow multiple manufacturers to support a
wider range of applications. I don't see how you can justify such a
broad claim about how this architecture will be used.
Ok, point taken.
I mentioned a scenario for systems 'running', not all who 'will run'
(or 'might run') for which your claim is correct.
Also, again there's good reason for the defconfigs to have HZ=100,
and that to be kept as is by many distros out there.
Well, the defconfig for x86 has HZ=1000, but we don't follow that
either. We picked something in the middle of the range of options and
we are consistent across architectures.
I see. I think this goes back to your point of 'a wider range of
applications', in the sense I mention defconfigs of pseries, which is
/one/ application of the kernel.
I wouldn't know all the reasons, but that's been thought by talented
people, for this platform. So I'd ask you to keep HZ=100 on Debian too.
Is that ok?
I can look for more evidence/explanations if you'd like.
I think this does need more explanation.
Ok, sure. I'll follow up.
Thanks,
--
Mauricio Faria de Oliveira
IBM Linux Technology Center
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