Re: [BUG] rebuild_sched_domains considered dangerous

On 04/20/2011 05:01 PM, Benjamin Herrenschmidt wrote:

On Wed, 2011-04-20 at 12:07 +0200, Peter Zijlstra wrote:

quoted

On Thu, 2011-03-10 at 15:10 +0100, Peter Zijlstra wrote:

quoted

Also, still waiting to hear from the Power7 folks on how often
they think to rebuild the topology and how they think that makes
sense, afaict Power7 does have actual NUMA nodes unlike s390, so
I'm still not seeing how that's going to work properly at all.

Jesse care to answer? I hear from Ben you're responsible for that
mess.

"responsible for this mess" is a big word :-)

But he's the one to last play with that code ... Jesse ?

Hi Peter!

According the the Power firmware folks, updating the home node of a virtual cpu happens rather infrequently. The VPHN code currently checks for topology updates every 60 seconds, but we can poll less frequently if it helps. I chose 60 second intervals simply because that's how often they check the topology on s390. ;-)

As for updating the memory topology, there are cases where changing the home node of a virtual cpu doesn't affect the memory topology. If it does, there is a separate notification system for memory topology updates that is independent from the cpu updates. I plan to start working on a patch set to enable memory topology updates in the kernel in the coming weeks, but I wanted to get the cpu patches out on the list so we could start having these debates. :)

Sincerely,

Jesse Larrew
Software Engineer, Linux on Power Kernel Team
IBM Linux Technology Center
Phone: (512) 973-2052 (T/L: 363-2052)
jlarrew@linux.vnet.ibm.com