Re: Benchmarking on CentOS 5

[Andrea Arcangeli <andrea@qumranet.com>]

On Wed, May 28, 2008 at 11:48:21AM -0600, Cam Macdonell wrote:
>
> Hi,
>
> I wanted to some benchmarking on a CentOS 5 host.  However, the warning in 
> dmesg about preempt notifiers indicates I shouldn't benchmark.  Is there a 
> workaround (aside from updating the kernel) that handles the issue?

The problem is that the preempt notifier emulation through hardware
breakpoints is worse at optimizing lightweight vm exists than the real
preempt notifiers supported by recent kernels. If you benchmark
without upgrading the kernel, it has to be clear it is running slower
than it would on a recent optimized host kernel. If you decide to
upgrade and compile the host kernel yourself, you need to configure it
with CONFIG_KVM=m to be sure the preempt notifiers are enabled in the
host kernel and in turn the printk will go away.

Thanks!