Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu access overhead

Eric Dumazet
2007-11-12T20:15:32Z

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.