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SubjectRe: [PATCH 0/4] pending scheduler updates

* Mike Galbraith <> wrote:

> On Wed, 2008-10-22 at 12:03 +0200, Mike Galbraith wrote:
> > It has positive effects too, but IMHO, the bad outweigh the good.
> BTW, most dramatic on the other end of the spectrum is pgsql+oltp.
> With preemption as is, it collapses as load climbs to heavy with
> preemption knobs at stock. Postgres uses user-land spinlocks and
> _appears_ to wake others while these are still held. For this load,
> there is such a thing as too much short-term fairness, preempting lock
> holder creates nasty gaggle of contended lock spinners. It's curable
> with knobs, and I think it's postgres's own fault, but may be wrong.
> With that patch, pgsql+oltp scales perfectly.

hm, tempting.

Have you tried to hack/fix pgsql to do proper wakeups?

Right now pgsql it punishes schedulers that preempt it while it is
holding totally undeclared (to the kernel) user-space spinlocks ...

Hence postgresql is rewarding a _bad_ scheduler policy in essence. And
pgsql scalability seems to fall totally apart above 16 cpus - regardless
of scheduler policy.


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