commit 74b717d93fd99fc8fefd98c6710c225c1be74363
Author: Ryota Ozaki <ozaki-r@iij.ad.jp>
Date:   Thu Sep 1 15:38:40 2016 +0900

    Add -falign-functions=16 to amd64 kernels
    
    This option aligns the start of functions by 16 bytes, which
    reduces performance fluctuations by small, unrelated changes.

diff --git a/sys/arch/amd64/conf/Makefile.amd64 b/sys/arch/amd64/conf/Makefile.amd64
index c1455c1..af748f2 100644
--- a/sys/arch/amd64/conf/Makefile.amd64
+++ b/sys/arch/amd64/conf/Makefile.amd64
@@ -42,6 +42,9 @@ CFLAGS+=	-mno-red-zone -mno-mmx -mno-sse -mno-avx
 CFLAGS+=	-msoft-float
 # For gcc we might need this, but other compilers barf
 # CFLAGS+=	-mno-fp-ret-in-387
+# Prevent the start of functions from varying by small, unrelated changes;
+# the variation causes performance fluctuations.
+CFLAGS+=	-falign-functions=16
 
 ##
 ## (3) libkern and compat