Re: [reiserfs-list] Re: [PATCH] Significant performace improvements on reiserfs systems

[Alan Cox]

> In Solaris, before spinning on a busy spin-lock, thread checks whether
> spin-lock holder runs on the same processor. If so, thread goes to sleep
> and holder wakes it up on spin-lock release. The same, I guess is going

> for interrupts that are served as separate threads. This way, one can
> re-schedule with spin-locks held.

This is one of the things interrupt handling by threads gives you, but the
performance cost is not nice. When you consider that ksoftirqd when it
kicks in (currently far too often) takes up to 10% off gigabit ethernet
performance, you can appreciate why we don't want to go that path.

Our spinlock paths are supposed to be very small and predictable. Where 
there is sleeping involved we have semaphores.

As lockmeter shows we still have a few io_request_lock cases at least where
we lock for far too long

Alan