This patch-set deals with an interesting yet stupid problem: kernel code that does not get inlined despite its simplicity. There are several causes for this behavior: "cold" attribute on __init, different function optimization levels; conditional constant computations based on __builtin_constant_p(); and finally large inline assembly blocks. This patch-set deals with the inline assembly problem. I separated these patches from the others (that were sent in the RFC) for easier inclusion. The problem with inline assembly is that inline assembly is often used by the kernel for things that are other than code - for example, assembly directives and data. GCC however is oblivious to the content of the blocks and assumes their cost in space and time is proportional to the number of the perceived assembly "instruction", according to the number of newlines and semicolons. Alternatives, paravirt and other mechanisms are affected, causing code not to be inlined, and degrading compilation quality in general. The solution that this patch-set carries for this problem is to create an assembly macro, and then call it from the inline assembly block. As a result, the compiler sees a single "instruction" and assigns the more appropriate cost to the code. In addition, this patch-set removes unneeded new-lines from common x86 inline asm's, which "confuse" GCC heuristics. Overall this patch-set slightly increases the kernel size (my build was done using my localmodconfig + localyesconfig for the record): text data bss dec hex filename 18126699 10066728 2936832 31130259 1db0293 ./vmlinux before 18148888 10064016 2936832 31149736 1db4ea8 ./vmlinux after (+0.06%) The patch-set eliminates many of the static text symbols: Before: 40033 After: 39650 (-1%) A microbenchmark with a loop of page-fault and MADV_DONTNEED show 2% performance improvement with this patch-set (when PTI is off). Changes from RFC: - Better formatting [Jan] - i386 build problems [0-day] - Inline comments - Separating __builtin_constant_p() into a different future patch-set Cc: Alok Kataria <akataria@xxxxxxxxxx> Cc: Christopher Li <sparse@xxxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jan Beulich <JBeulich@xxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: linux-sparse@xxxxxxxxxxxxxxx Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx Cc: x86@xxxxxxxxxx Nadav Amit (6): x86: objtool: use asm macro for better compiler decisions x86: bug: prevent gcc distortions x86: alternative: macrofy locks for better inlining x86: prevent inline distortion by paravirt ops x86: refcount: prevent gcc distortions x86: removing unneeded new-lines arch/x86/include/asm/alternative.h | 34 +++++++++++---- arch/x86/include/asm/asm.h | 4 +- arch/x86/include/asm/bug.h | 56 ++++++++++++++++-------- arch/x86/include/asm/cmpxchg.h | 10 ++--- arch/x86/include/asm/paravirt_types.h | 63 +++++++++++++++++---------- arch/x86/include/asm/refcount.h | 62 ++++++++++++++++---------- arch/x86/include/asm/special_insns.h | 12 ++--- include/linux/compiler.h | 37 ++++++++++++---- 8 files changed, 183 insertions(+), 95 deletions(-) -- 2.17.0 -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
