Re: Negative scalability by removal of lock_kernel()?(Was: Strange performance behavior of 2.4.0-test9)

Andi Kleen
2000-10-27T10:26:15Z

On Fri, Oct 27, 2000 at 09:23:56PM +1100, Andrew Morton wrote:
> Andi Kleen wrote:
> >
> > When you have two CPUs contending on common paths it is better to do:
> > [ spinlock stuff ]
>
> Andi, if the lock_kernel() is removed then the first time the CPUs will butt heads is on a semaphore. This is much more expensive.
>
> I bet if acquire_fl_sem() and release_fl_sem() are turned into lock_kernel()/unlock_kernel() then the scalability will come back.

To test your theory it would be enough to watch context switch rates in top

-Andi