On 05/18/2012 07:57 AM, Ingo Molnar wrote:
* tip-bot for Peter Zijlstra<a.p.zijlstra@xxxxxxxxx> wrote:Commit-ID: 84213e2b6e2166083c3d06e91dcf54f8e136bd78 Gitweb: http://git.kernel.org/tip/84213e2b6e2166083c3d06e91dcf54f8e136bd78 Author: Peter Zijlstra<a.p.zijlstra@xxxxxxxxx> AuthorDate: Sat, 3 Mar 2012 17:05:16 +0100 Committer: Ingo Molnar<mingo@xxxxxxxxxx> CommitDate: Fri, 18 May 2012 08:16:20 +0200 sched, mm: Introduce tsk_home_node()So, I wanted to see some progress on this issue and committed Peter's 'home node NUMA affinity' changes to the tip:sched/numa tree. Basically the scheme Peter implemented is an extended notion of NUMA affinity, one that both the scheduler and the MM honors - but one that is flexible and treats affinity as a preference, not as a hard mask: - For example if there's significant idle time on distant CPUs then the scheduler will still utilize those CPUs and fill the whole machine - but otherwise the scheduler and the MM will try to maintain good NUMA locality. - Similary, memory allocations will go to the home node even if the task is running on another node temporarily. [as long as the allocation can be satisfied.] This is a more dynamic, more intelligent version of hard partitioning the system and workloads between NUMA nodes - yet it is pretty simple and existing MM and scheduling code mostly support this scheme and needed only small reorganization. When home node awareness is active then applications can use new system calls to group themselves into affinity groups, via: sys_numa_tbind(tid, -1, 0); // create new group, return new ng_id sys_numa_tbind(tid, -2, 0); // returns existing ng_id sys_numa_tbind(tid, ng_id, 0); // set ng_id ... and to assign memory to a NUMA group: sys_numa_mbind(addr, len, ng_id, 0); We are seeing user-space daemons trying to achieve something similar, for example there's "numad": https://fedoraproject.org/w/index.php?title=Features/numad&oldid=272815 the kernel is in a much better position to handle affinities and resource allocation preferences, especially ones that change and mix so dynamically as scheduling and memory allocation - so maybe "numad" could make use of the new syscalls and map application/package policies into NUMA groups the kernel recognizes.
Thanks for the cc on this. I have cc'ed Bill Gray who authored numad and will leave it to him to comment on the interfaces, but indeed this has been something that we have been looking for, the concept of a home node (or nodes). cheers, Bill (Burns)
(There's more such daemons out there, in the HPC area.) One configurability detail I'd like to suggest to Peter: could we make this NUMA affinity grouping capability unconditional to apps, i.e. enable apps to put themselves on home node aware policy even if the sysctl is off? That way this capability would always be available on NUMA systems in an opt-in fashion, just like regular affinities are available. The sysctl would merely control whether all tasks on the system are scheduled in a home node aware fashion or not. (and it would still default to off) Thanks, Ingo
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