LWN: Comments on "The new NUMA scheduler"

The new NUMA scheduler

hbaum — Wed, 29 Jan 2003 17:12:39 +0000

The NUMA scheduler patches that have been around since October consisted of two pieces - balance-on-exec, and NUMA-aware-load-balance. The three line patch that Martin wrote replaced the NUMA-aware-load-balance, but still relied on the balance-on-exec patch being in place. So it is not accurate to state that the NUMA scheduler patch which provided equivalent performance to the original NUMA scheduler patch was simply a three line patch. Rather one half of the original NUMA scheduler patch was replaced by a three line patch. The balance-on-exec portion of the NUMA scheduler patch was still required to get equivalent performance.

Regarding something like this going in after feature freeze - with Martin's contribution, the NUMA scheduler changes have no impact on non-NUMA systems. The balance-on-exec portion of the patch was always a NUMA only piece of code, and Martin's contribution removed the need for an invasive change to the load balancer.

three-line patch?

mbligh — Thu, 23 Jan 2003 21:27:52 +0000

I wrote the "3-line" patch to show how non-invasive a NUMA scheduler could be. It also changes the design of the NUMA scheduler to become a set of "concentric circles" as far as load-balance is concerned - I think this is a better design.

IMO, in the post-freeze environment, the only way to proceed is small, well contained patches that obviously don't break anyone else ...

three-line patch?

corbet — Thu, 23 Jan 2003 03:02:05 +0000

Sorry, I should have been more explicit there. The patch was by Martin Bligh, who has been working with the NUMA scheduler for a while. Here's a copy with his explanation of what's going on.

three-line patch?

cpeterso — Thu, 23 Jan 2003 02:54:20 +0000

I am a little confused about the origin of the "three-line patch". Was that patch taken from the ongoing NUMA schduler work? Or was it written by an "outsider" who demonstrated the same benefits as the "big" NUMA scheduler, but with far fewer lines of code?