Re: [PATCH 0/4] pending scheduler updates

[Ingo Molnar <mingo@elte.hu>]

* Mike Galbraith <efault@gmx.de> wrote:

> > > With that patch, pgsql+oltp scales perfectly.
> > 
> > hm, tempting.
> 
> I disagree.  Postgres's scaling problem is trivially corrected by 
> twiddling knobs (or whatnot). [...]

okay, then we need to document it a bit more: what knobs need twiddling 
to make it scale perfectly?

> [...]  With that patch, you can't twiddle mysql throughput back, or 
> disk intensive loads for that matter.  You can tweak the preempt 
> number, but it has nothing to do with lag, so anybody can preempt 
> anybody else as you turn the knob toward zero.  Chaos.

okay, convinced.

> > Have you tried to hack/fix pgsql to do proper wakeups?
> 
> No, I tried to build without spinlocks to verify, but build croaked. 
> Never went back to slogging through the code.

if it falls back to IPC semaphores that's a bad trade from a performance 
POV. The best would be if it used proper futexes (i.e. pthread_mutex() 
and friends) not some home-grown user-space spinlock thing.

	Ingo