Messages in this thread | | | Date | Mon, 17 Mar 2008 10:32:15 -0700 (PDT) | From | Christoph Lameter <> | Subject | Re: hackbench regression since 2.6.25-rc |
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On Mon, 17 Mar 2008, Zhang, Yanmin wrote:
> slub_min_objects | 8 | 16 | 32 | 64 > -------------------------------------------------------------------------------------------- > slab(__slab_alloc+__slab_free+add_partial) cpu utilization | 88.00% | 44.00% | 13.00% | 12% > > > When slub_min_objects=32, we could get a reasonable value. Beyond 32, the improvement > is very small. 32 is just possible_cpu_number*2 on my tigerton.
Interesting. What is the optimal configuration for your 8p? Could you figure out the optimal configuration for an 4p and a 2p configuration?
> It's hard to say hackbench simulates real applications closely. But it discloses a possible > performance bottlebeck. Last year, we once captured the kmalloc-2048 issue by tbench. So the > default slub_min_objects need to be revised. In the other hand, slab is allocated by alloc_page > when its size is equal to or more than a half page, so enlarging slub_min_objects won't create > too many slab page buffers. > > As for NUMA, perhaps we could define slub_min_objects to 2*max_cpu_number_per_node.
Well for a 4k cpu configu this would set min_objects to 8192. So I think we could implement a form of logarithmic scaling based on cpu counts comparable to what is done for the statistics update in vmstat.c
fls(num_online_cpus()) = 4
So maybe
slub_min_objects= 8 + (2 + fls(num_online_cpus())) * 4
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