On Thursday 24 May 2007 12:29 pm, Jan Engelhardt wrote: > > On May 23 2007 23:22, Adrian Bunk wrote: > > > >And we need only two different inline levels (__always_inline and > >"let the compiler decide"), not three (__always_inline, inline and > >"let the compiler decide"). > > "inline" is "let the compiler decide".
The compiler decides anyway. That's why we need a noinline to tell it _not_ to spontaneously inline things it shouldn't. > If it is not, then it is "let the > compiler decide, based on my bias that I think it should be inlined". Things like unlikely() actually produce different code (and are, technically speaking, workarounds for the high branch misprediction penalty in modern processor designs). Things like "register" are a hint to the compiler that it's free to ignore. How often do we use the "register" keyword in Linux? Register allocation is totally different on different processors, and deprived of context the hint is almomst meaningless. If it doesn't guarantee anything and has far less of a performance impact than the difference between -O2 and -Os (or between gcc 3.4 and 4.1), then it's probably an unnecessary complication. Inlining is even worse because whether or not it's a performance win depends on the L1 cache size, cache line size and alignment, L2 cache, DRAM fetch latency, and so on. This varies all over the map within a given processor line, let alone between processors. If we actually need something inlined, we can tell it to do so reliably with __always_inline (and change __always_inline to be MORE explicit each time gcc breaks the previous way of saying "yes really inline it dammit"). If we can live with it not being inlined, why not leave it to the compiler whether or not to inline it? Rob - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
