What is the PREEMPTION option good for?

[Ivan Voras]

Ivan Voras wrote:
> Bruce Evans wrote:
> 
>> Most of the difference is caused by pgzero becoming too active with
>> PREEMPTION.  
> 
> Don't know about the other things but I've noticed pagezero is
> suspiciously active on heavy loaded SMP web servers (even complained on
> @stable a long time ago). I'll try disabling PREEMPTION and see how it goes.

Ok, I couldn't run extensive tests because people were waiting to use
the machine, so this should be considered anecdotal evidence. On a
simple benchmark that repeatedly (for 1 minute) and concurrently
(target=50 concurrent requests) hits a dynamic web page on a development
machine (2 proc true SMP), the performance goes up from ~85
requests/sec. to ~105 requests/s by disabling PREEMPTION. This
improvement looks suspiciously high to me, but I don't think I'll be
going back :) pagezero is now not noticable in 'top' output.