Re: [benchmark] 1% performance overhead of paravirt_ops on native kernels

[Pekka Enberg <penberg@cs.helsinki.fi>]

Hi Chris,

On Tue, Jun 2, 2009 at 8:03 AM, Chris Mason <chris.mason@oracle.com> wrote:
>>> The best place to fix xen is in the kernel.

On Tue, Jun 02, 2009 at 08:22:57AM -0700, Ulrich Drepper wrote:
>> No.  The best way to fix things is _on the way into the kernel_.

On Tue, Jun 2, 2009 at 7:20 PM, Chris Mason <chris.mason@oracle.com> wrote:
> It all depends on which parts are causing problems.  A 1% performance
> hit, under a CONFIG_ that can be disabled?  If maintainers are focusing
> on details like this for long term and active projects, we're doing
> something very wrong.

The fact that CONFIG_PARAVIRT can be disabled doesn't really help. As
a matter of fact, I'd argue that one of the primary reasons
CONFIG_SLUB regression is still there is because people can just
disable it and use CONFIG_SLAB instead.

So I think we have some evidence to suggest that people have less
incentive to fix things once something is merged to the kernel. And I
don't mean the authors of the code here but basically _everyone_
involved in kernel development. It usually takes effort from variety
of people to get everything ironed out because, lets face it, we can't
expect a handful of people to test out every configuration let alone
fix them.

                        Pekka