> Would the examples (page copy, page clear) be an okay place to do it? > These sections can't be preempted anyway (right?), and it's noted that > doing it with AltiVec is a tad faster than using MMU tricks or standard > copies?
I think typically page copying and clearing -are- preemptible. I'm not sure what you mean by MMU tricks, but it's not clear whether using altivec will result in any significant performance gain here, considering the cost of enabling/disabling altivec (added to handling the preemption issue). However, nothing prevents you from trying to do it and we'll see what the results are with hard numbers. > In Scott's case, while "optimizing memcpy for 48byte blocks" was a joke, > this is 3 load/stores in AltiVec, which as long as every SKB is 16 > byte aligned (is there any reason why it would not be? :) In this case, the cost of enabling/saving/restoring altivec will far outweight any benefit. In addition, skb's are often not well aligned due to the alignment tricks done with packet headers. > skb_clone might not be something you want to dump AltiVec into and would > make a mess if an skb got extended somehow, but the principle is outlined > in a very good document from a very long time ago; > > http://www.motorola.com.cn/semiconductors/sndf/conference/PDF/AH1109.pdf > > I think a lot of it still holds true as long as you really don't care > about preemption under these circumstances (where network throughput > is more important, and where AltiVec actually *reduces* CPU time, the > overhead of disabling preemption is lower anyway). You could say the > same about the RAID functions - I bet LatencyTOP has a field day when > you're using RAID5 AltiVec. RAID6 actually :-) In any case, as I said, people are welcome to implement something that can be put to the test and measured. If it proves beneficial enough, then I see no reason not to merge it. Basically, enough talks, just do something and we'll see whether it proves useful or not. Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
