Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to3.6-rc5 on AMD chipsets - bisected

[Alan Cox]

> Yes, postgress performs loads better with it's spinlocks, but due to
> that, it necessarily _hates_ preemption.  How the is the scheduler
> supposed to know that any specific userland task _really_ shouldn't be
> preempted at any specific time, else bad things follow?

You provide a shared page for a process group so it can write hints to
which is kernel mapped so the scheduler can peek..

Alan
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