On Sun, Jan 26, 2025 at 05:47:08PM +0100, Vlastimil Babka wrote: > On 1/26/25 08:02, Suren Baghdasaryan wrote: > > When a sizable code section is protected by a disabled static key, that > > code gets into the instruction cache even though it's not executed and > > consumes the cache, increasing cache misses. This can be remedied by > > moving such code into a separate uninlined function. The improvement > > Weird, I thought the static_branch_likely/unlikely/maybe was already > handling this by the unlikely case being a jump to a block away from the > fast-path stream of instructions, thus making it less likely to get cached. > AFAIU even plain likely()/unlikely() should do this, along with branch > prediction hints. Very much depends on the compiler :-( sometimes unlikely just moves it to the end of the function, sometimes it's moved to .text.unlikely. Some compilers have label attributes: l_yes: __attribute__((cold)); but the same compilers utterly ignore it when it's combined with asm-goto or something -- we could never get it to work reliably. It's been a while since I looked at this, so I'm not entirely sure what the current version of compilers do.
