Re: Fw: potential /dev/urandom scalability improvement

[Matt Mackall <mpm@selenic.com>]

On Thu, Mar 25, 2004 at 06:00:14PM -0800, Andrew Morton wrote:
> David Mosberger <davidm@napali.hpl.hp.com> wrote:
> >
> > The
> >  patch below is updated to go on top of your patch and gives about the
> >  same performance as I reported yesterday.  For now, I defined an
> >  inline prefetch_range().  If and when all architectures get updated to
> >  define this directly, we can simply remove prefetch_range() from the
> >  driver.
> 
> We may as well stick prefetch_range() in prefetch.h.
> 
> And Matt's patch series is not a thing I want to take on board at present,
> so let's stick with the straight scalability patch for now.

Sigh, I'll trim it back to some bits I think are critical.
 
> I moved the prefetch_range() call to outside the spinlock.  Does that make
> sense?

I don't think that's actually a win. If there's contention, threads
racing to the lock will grab the same cache lines and all but one
thread's cache will end up invalidated by the time the lock is
released.

-- 
Matt Mackall : http://www.selenic.com : Linux development and consulting