On Sun, Nov 24, 2019 at 04:19:16PM -0800, Linus Torvalds wrote: > It looks from profiles like ext4_getattr() is fairly expensive, > because it unnecessarily accesses the extended inode information and > causes extra cache misses. > > On an empty kernel allmodconfig build (which is a lot of "stat()" > calls by Make, and a lot of silly string stuff in user space due to > all the make variable games we play), ext4_getattr() was something > like 1% of the time according to the profile I gathered. It might be > bogus - maybe the cacheline ends up being accessed later anyway, but > it _looked_ like it was the whole "i_extra_isize" access that missed > in the cache. > > That's all for gathering the STATX_BTIME information, that the caller > doesn't even *want*. > > How about a patch like the attached? Looks good, thanks, I've applied it to the ext4 tree. I'm a bit surprised a cache line miss rated that high on a kernel build, but that probably says a lot about how efficient the rest of the kernel was (and I assume Make didn't need to rebuild most of the object files). - Ted P.S. Did you see the ext4 pull request? I wasn't sure if you haven't gotten to it yet due to being distracted by Turkey day or not...
