Re: Wierd context-switching issue on Xeon

Tom,

> Strictly a WAG ... but what this sounds like to me is disastrously bad
> behavior of the spinlock code under heavy contention.  We thought we'd
> fixed the spinlock code for SMP machines awhile ago, but maybe
> hyperthreading opens some new vistas for misbehavior ...

Yeah, I thought of that based on the discussion on -Hackers.  But we tried
turning off hyperthreading, with no change in behavior.

> If you can't try 7.4, or want to gather more data first, it would be
> good to try to confirm or disprove the theory that the context switches
> are coming from spinlock delays.  If they are, they'd be coming from the
> select() calls in s_lock() in s_lock.c.  Can you strace or something to
> see what kernel calls the context switches occur on?

Might be worth it ... will suggest that.  Will also try 7.4.

--
-Josh Berkus
 Aglio Database Solutions
 San Francisco