Anyone rolling a kernel nowadays?

James Hogarth james.hogarth at gmail.com
Mon Aug 9 21:21:25 UTC 2010


>
> Yes there is a significant amount of overhead removed with custom
> kernels, especially on servers where we need that overhead removed so
> that we can utilize the hardware as much as we can.  You can also do
> some basic optimizations in /etc/sysctl.conf
>


I'd love to see some actual benchmarks done.... given how 'cheap'
hardware is in a general sense (and of course this depends upon one's
application profile) if you are pushing your systems that close to the
edge that you need effectively do a respin of the distribution to get
the performance required (and the added time and therefore cost in
maintaining that especially over multiple systems) I'd be more worried
about growth going forwards for that application and the surrounding
issues of failure plans.....

>From a pure upstream point of view Red Hat (and CentOS... I'd assume
Canonical but I haven't discussed the issue with them) will not spend
time on bugs that are potentially linked to a custom kernel -
filesystem, network etc. The response will simply be to duplicate the
issue on a stock kernel as provided by them and then file a bug report
on that.... the same will be said from proprietary vendors such as
Oracle.

As an admin who would rather be able to file a bug and then get on
with more pressing issues... well that's why I overspec my hardware a
bit (with growth in mind) and then monitor performance on that with a
'supported' setup rather then spend days (potentially to get accurate
figures) tweaking small options and profiling repeatedly to tune every
teeny instruction cycle from the system.... especially when properly
indexed, denormalised and optimised queries (for a database example)
will usually make more difference than compiling to remove unnecessary
options in the kernel... doubly so given most things in distribution
support kernels tend to be modules and thus only loaded as
required....

Factor in as well that even in gentoo systems with *everything*
compiled from source with optimised flags will not always see that
much more performance dependant on workload... and even if your kernel
is custom compiled -O3 M x86_64 --pipe-lined yada yada etc etc the
rest of your executables/libraries on the system almost certainly are
not for Ubuntu/Redhat ;)

James




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