Re: [PATCH] Significant performace improvements on reiserfs systems

Robert Love
2001-09-21T03:14:29Z

On Thu, 2001-09-20 at 21:20, Andrew Morton wrote:
> This may not be practical.
>
> Take, for example, zap_page_range(). It simply has a lot
> of work to do, and it does it inside a spinlock. By doing
> it in a tight loop, it's optimal.
>
> There is no way to speed this function up by two or three orders
> of magnitude. (Well, there is: don't take the lock at all if
> the mm isn't shared, but this is merely an example. There are
> other instances).

Agreed, but...

> It seems that for a preemptive kernel to be successful, we need
> to globally alter the kernel so that it never holds locks for
> more than 500 microseconds. Which is what the conditional_schedule()
> (aka cooperative multitasking :)) patches do.
>
> It seems that there are no magic bullets, and low latency will
> forever have a global impact on kernel design, unless a way is
> found to reschedule with locks held. I recall that a large
> part of the MontaVista patch involved turning spinlocks into
> semaphores, yes? That would seem to be the way to go.

This would be the situation that solved the problem with little
complaint, huh?

--
Robert M. Love
rml at ufl.edu
rml at tech9.net