> On Feb 27, 2019, at 2:12 AM, Peter Zijlstra <pet...@infradead.org> wrote: > > Hi all, > > This is a collection of x86/percpu changes that I had pending and got reminded > of by Linus' comment yesterday about __this_cpu_xchg(). > > This tidies up the x86/percpu primitives and fixes a bunch of 'fallout'. > > Built and boot tested with CONFIG_DEBUG_PREEMPT=y.
Overall this series affects 70 functions and shortens the code by 326 bytes. _local_bh_enable() for example is shorten by 14 bytes (26%). I must admit that I although I pointed some of these issues before, I am not sure whether they are really important... Recently, I tried to see how to make the compiler to generate “better code” from Linux. I sprinkled “pure” attribute on many common function (e.g., page_rmapping()), sg_next()); sprinkled const-attribute on some others (e.g., jiffies_to_msecs()); created a const-alias variable so the compiler would consider kaslr variables and sme_me_mask as constant after initialization, and so on. I was then looking at the changed code, and while some functions were shorter and some longer, many common functions did look “better”. The only problem was that any benchmark that I did not show any measurable impact. So perhaps it is a matter of measurement, but eventually right now there is no clean win.
