Messages in this thread | | | From | Jesse Barnes <> | Subject | Re: RCU scaling on large systems | Date | Mon, 3 May 2004 09:39:11 -0700 |
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On Sunday, May 2, 2004 11:28 am, Paul E. McKenney wrote: > From your numbers below, I would guess that if you have at least > 8 CPUs per NUMA node, a two-level tree would suffice. If you have > only 4 CPUs per NUMA node, you might well need a per-node level, > a per-4-nodes level, and a global level to get the global lock > contention reduced sufficiently.
Actually, only 2, but it sounds like your approach would work.
> Cute! However, it is not clear to me that this approach is > compatible with real-time use of RCU, since it results in CPUs > processing their callbacks less frequently, and thus getting > more of them to process at a time.
I think it was just a proof-of-concept--the current RCU design obviously wasn't designed with this machine in mind :).
> But it is not clear to me that anyone is looking for realtime > response from a 512-CPU machine (yow!!!), so perhaps this > is not a problem...
There are folks that would like realtime (or close to realtime) response on such systems, so it would be best not to do anything that would explicitly prevent it.
> This patch certainly seems simple enough, and I would guess that > "jiffies" is referenced often enough that it is warm in the cache > despite being frequently updated. > > Other thoughts?
On a big system like this though, won't reading jiffies frequently be another source of contention?
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