Re: [Patch 3/3] prepopulate/cache cleared pages

[Andi Kleen <ak@suse.de>]

On Friday 24 February 2006 10:26, Nick Piggin wrote:

> [aside]
> Actually I have a scalability improvement for rwsems, that moves the
> actual task wakeups out from underneath the rwsem spinlock in the up()
> paths. This was useful exactly on a mixed read+write workload on mmap_sem.
> 
> The difference was quite large for the "generic rwsem" algorithm because
> it uses the spinlock in fastpaths a lot more than the xadd algorithm. I
> think x86-64 uses the former, which is what I presume you're testing with?

I used the generic algorithm because Andrea originally expressed some doubts 
on the correctness of the xadd algorithms and after trying to understand them 
myself I wasn't sure myself. Generic was the safer choice.

But if someone can show convincing numbers that XADD rwsems are faster
for some workload we can switch. I guess they are tested well enough now
on i386.

Or would your scalability improvement remove that difference (if it really exists)?


-Andi