Hi Nick, > I've got a patch that makes alternate feature patching a bit > more flexible and not hit relocation limits when using big "else" > parts. I was thinking of doing something like > > _GLOBAL_TOC(copy_page) > BEGIN_FTR_SECTION_NESTED(50) > #include "copypage_power9.S" > FTR_SECTION_ELSE_NESTED(50) > #include "copypage_power7.S" > ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_ARCH_300, 50)
Good idea, I hadn't thought of embedding it all in a feature section. > I guess POWER asm doesn't need this but it's good practice to prevent > copy paste errors? It would be nice to have some macros to hide all > these constants, but that's for another patch. The commenting is good. The .machine X macros? Unfortunately the format of dcbt is different for recent server chips. This wasn't a great idea in retrospect because if you do get the instruction layout wrong, you wont get a fault to warn you. > I don't suppose the stream setup is costly enough to consider > touching a cacheline or two ahead before starting it? Starting up software streams is a bit of an art - if the demand loads get ahead then a hardware stream gets started before the software one. Note all the eieios to try and avoid this happening. I've struggled with software prefetch on previous chips and sometimes I wonder if it is worth the pain. > (Also for another day) We might be able to avoid the stack and call > for some common cases. Pretty small overcall cost I guess, but it > could be beneficial for memcpy if not copy_page. Definitely. Also the breakpoint for using vector should be much lower if we have already saved the user state in a previous call. Anton