[aklug] Re: Compiling the kernel for the Dell Mini 10v

From: Arthur Corliss <acorliss@nevaeh-linux.org>
Date: Sun Sep 27 2009 - 08:45:27 AKDT

On Sun, 27 Sep 2009, Shane Spencer wrote:

> Most modern distro configs specify the HZ as well as the NO_HZ config
> variable. Chances are changing from 1000 to 300 will do nothing since
> NO_HZ talkes precedence AFAIK.
>
> There's lots of good info on the webs on CONFIG_CC_OPTIMIZE_FOR_SIZE
> and the benefits it offers many targets. The kernel I'm using doesn't
> enable it because it's expected to run on systems with P4 like chips
> with a large cache. I don't know how large the executable is once
> loaded, but the compressed kernel image is only 3.4M.

HZ still has an effect, even in tickless kernels. Desktop systems and
virtualization hosts should tend towards high HZ values in order to reduce
latencies. General purpose servers and VM hosts, however, should tend
towards lower VM values.

I always use size optimization myself. Cache coherency in general is a big
deal for performance, even more so when you're running multiple VMs. And
most people don't understand that gcc's "performance" optimization can not
only introduce some bugs, but kill you with much larger kernels (especially
optimizations like loop unrolling), which, again, devestates cache
coherency. Which is why many projects rarely use higher than '-O2'.

         --Arthur Corliss
           Live Free or Die
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Received on Sun Sep 27 08:45:40 2009

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