Messages in this thread | | | Date | Mon, 12 Nov 2007 21:14:47 +0100 | From | Eric Dumazet <> | Subject | Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu access overhead |
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Luck, Tony a écrit : >>> Ahh so the need to be able to expand per cpu memory storage on demand >>> is not as critical as we thought. >>> >> Yes, but still desirable for future optimizations. >> >> For example, I do think using a per cpu memory storage on net_device refcnt & >> last_rx could give us some speedups. > > We do want to keep a very tight handle on bloat in per-cpu > allocations. By definition the total allocation is multiplied > by the number of cpus. Only ia64 has outrageous numbers of > cpus in a single system image today ... but the trend in > multi-core chips looks to have a Moore's law arc to it, so > everyone is going to be looking at lots of cpus before long. >
I dont think this is a problem. Cpus numbers and ram size are related, even if Moore didnt predicted it;
Nobody wants to ship/build a 4096 cpus machine with 256 MB of ram inside. Or call it a GPU and dont expect it to run linux :)
99,9% of linux machines running on earth have less than 8 cpus and less than 1000 ethernet/network devices.
In case we increase the number of cpus on a machine, the limiting factor is the fact that cpus have to continually exchange on memory bus those highly touched cache lines that contain refcounters or stats.
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