Messages in this thread | | | Date | Tue, 13 Nov 2012 08:24:41 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 0/8] Announcement: Enhanced NUMA scheduling with adaptive affinity |
| |
* Christoph Lameter <cl@linux.com> wrote:
> On Mon, 12 Nov 2012, Peter Zijlstra wrote: > > > The biggest conceptual addition, beyond the elimination of > > the home node, is that the scheduler is now able to > > recognize 'private' versus 'shared' pages, by carefully > > analyzing the pattern of how CPUs touch the working set > > pages. The scheduler automatically recognizes tasks that > > share memory with each other (and make dominant use of that > > memory) - versus tasks that allocate and use their working > > set privately. > > That is a key distinction to make and if this really works > then that is major progress.
I posted updated benchmark results yesterday, and the approach is indeed a performance breakthrough:
http://lkml.org/lkml/2012/11/12/330
It also made the code more generic and more maintainable from a scheduler POV.
> > This new scheduler code is then able to group tasks that are > > "memory related" via their memory access patterns together: > > in the NUMA context moving them on the same node if > > possible, and spreading them amongst nodes if they use > > private memory. > > What happens if processes memory accesses are related but the > common set of data does not fit into the memory provided by a > single node?
The other (very common) node-overload case is that there are more tasks for a shared piece of memory than fits on a single node.
I have measured two such workloads, one is the Java SPEC benchmark:
v3.7-vanilla: 494828 transactions/sec v3.7-NUMA: 627228 transactions/sec [ +26.7% ]
the other is the 'numa01' testcase of autonumabench:
v3.7-vanilla: 340.3 seconds v3.7-NUMA: 216.9 seconds [ +56% ]
> The correct resolution usually is in that case to interleasve > the pages over both nodes in use.
I'd not go as far as to claim that to be a general rule: the correct placement depends on the system and workload specifics: how much memory is on each node, how many tasks run on each node, and whether the access patterns and working set of the tasks is symmetric amongst each other - which is not a given at all.
Say consider a database server that executes small and large queries over a large, memory-shared database, and has worker tasks to clients, to serve each query. Depending on the nature of the queries, interleaving can easily be the wrong thing to do.
Thanks,
Ingo
| |