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Hello, > > > details, but I do know that using copy_from_user() is not a real > > > improvement at least on x86 architecture. > > > > The same as bit is easy to explain. Its totally memory bandwidth limited > > on current x86-32 processors. (Although I'd welcome demonstrations to > > the contrary on newer toys) > > Nope. There are distinct alignment problems with movsl-based > memcpy on PII and (at least) "Pentium III (Coppermine)", which is > tested here: ... > I have various scriptlets which generate the entire matrix. > > I think I ended up deciding that we should use movsl _only_ > when both src and dsc are 8-byte-aligned. And that when you > multiply the gain from that by the frequency*size with which > funny alignments are used by TCP the net gain was 2% or something. Amazing! I beleived 4-byte-aligned was enough. read/write systemcalls may also reduce their penalties. > It needs redoing. These differences are really big, and this > is the kernel's most expensive function. > > A little project for someone. OK, if there is nobody who wants to do it I'll do it by myself. > The tools are at http://www.zip.com.au/~/linux/cptimer.tar.gz - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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