Messages in this thread | | | Subject | Re: [RFC][PATCH] x86, sched: allow topolgies where NUMA nodes share an LLC | From | Dave Hansen <> | Date | Thu, 9 Nov 2017 10:13:53 -0800 |
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On 11/09/2017 06:07 AM, Borislav Petkov wrote: > On Wed, Nov 08, 2017 at 04:00:38PM -0800, Dave Hansen wrote: >> I'd argue that those two end up looking pretty much the same to an app. >> The only difference is that the slice-local and slice-remote cache hits >> have slightly different access latencies. I don't think it's enough to >> notice. > > So if it is not enough to notice, why do we even bother? I.e., is > there any workload showing any advantages at all from the resources > partitioning?
If you want the *absolutely* best latency available, you turn on SNC. You get a small boost to slice-local access and a slight penalty to remote-slice access compared to when Sub-NUMA-Clustering is off.
You can measure this for sure, but I'll still say that most folks will never notice. In addition, if you have access interleaved everywhere, the "slice-local boost" and "remote-slice penalty" roughly cancel each-other out.
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