I'm experimenting with Kernel Preemption
davej at redhat.com
Wed May 11 21:01:08 UTC 2005
On Wed, May 11, 2005 at 02:17:25PM -0300, Juan Carlos Castro y Castro wrote:
> Not on Fedora's kernel sources, but with 2.6.11ac7. I based my config on
> /boot/config-2.6.11-1.14_FC3 and deat with the additional options with
> "make oldconfig". Then I browsed the configuration with "make
> menuconfig", just for fun.
> I saw kernel preemption was turned off, so I turned on. Afterwards, I
> notice the system is noticeably faster. Bootup is faster. Shutdown is
> faster. The Red Hat manu on GNOME pops up WAY faster. OpenOffice.org
> loading is faster. I suspect other things are faster too, but I'd have
> to time them.
Every time this comes up, theres no concrete numbers. Just
'it feels faster'. Given the best that preempt can do is
lower the _average_ latency, rather than worse-case latencies
which many folks believe, I find it hard to believe it makes
a noticable difference. In a blind-test, given two kernels,
I'd bet on you not being able to 'feel' which one had
> So my question is: why isn't preemption enabled in the FC3 packaged
> kernel? Does it conflict with something I haven't encountered yet? maybe
> some esoteric hardware combination? My hardware data is below.
It doesn't really buy anything worthwhile, and adds complexity and
opportunity for drivers to break.
> Another thing: what crucial patch, if any, am I missing by using
> 2.6.11ac7 instead of the FC3 packaged kernel?
Exec-shield is probably the biggest feature, but there are a bunch
of other minor features (restricted /dev/mem, ipw wireless for eg).
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