[PATCH 1/2] x86: separating entry text section

[Jiri Olsa <jolsa@redhat.com>]

Putting x86 entry code to the separate section: .entry.text.

Separating the entry text section seems to have performance
benefits with regards to the instruction cache usage.

Running hackbench showed that the change compresses the icache
footprint. The icache miss rate went down by about 8%:

before patch:
     26282174  L1-icache-load-misses      ( +-   0.099% )  (scaled from 81.00%)

after patch:
     24237651  L1-icache-load-misses      ( +-   0.117% )  (scaled from 80.96%)


Whole perf output follows.

- results for current tip tree:

 Performance counter stats for './hackbench/hackbench 10' (500 runs):

    817646684  L1-icache-loads            ( +-   0.150% )  (scaled from 80.99%)
     26282174  L1-icache-load-misses      ( +-   0.099% )  (scaled from 81.00%)
       211864  L1-icache-prefetches       ( +-   0.616% )  (scaled from 80.99%)
<not counted>  L1-icache-prefetch-misses
    817646737  iTLB-loads                 ( +-   0.151% )  (scaled from 80.98%)
        82368  iTLB-load-misses           ( +-   0.451% )  (scaled from 80.98%)

  0.206651959  seconds time elapsed   ( +-   0.152% )


- results for current tip tree with the patch applied are:

 Performance counter stats for './hackbench/hackbench 10' (500 runs):

    960162049  L1-icache-loads            ( +-   0.114% )  (scaled from 80.95%)
     24237651  L1-icache-load-misses      ( +-   0.117% )  (scaled from 80.96%)
       179800  L1-icache-prefetches       ( +-   0.530% )  (scaled from 80.95%)
<not counted>  L1-icache-prefetch-misses
    960352725  iTLB-loads                 ( +-   0.114% )  (scaled from 80.93%)
        84410  iTLB-load-misses           ( +-   0.491% )  (scaled from 80.92%)

  0.210509948  seconds time elapsed   ( +-   0.140% )


wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>
---
 arch/x86/ia32/ia32entry.S         |    2 ++
 arch/x86/kernel/entry_32.S        |    6 ++++--
 arch/x86/kernel/entry_64.S        |    6 ++++--
 arch/x86/kernel/vmlinux.lds.S     |    1 +
 include/asm-generic/sections.h    |    1 +
 include/asm-generic/vmlinux.lds.h |    6 ++++++
 6 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 0ed7896..50f1630 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -25,6 +25,8 @@
 #define sysretl_audit ia32_ret_from_sys_call
 #endif
 
+	.section .entry.text, "ax"
+
 #define IA32_NR_syscalls ((ia32_syscall_end - ia32_sys_call_table)/8)
 
 	.macro IA32_ARG_FIXUP noebp=0
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index c8b4efa..f5accf8 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -65,6 +65,8 @@
 #define sysexit_audit	syscall_exit_work
 #endif
 
+	.section .entry.text, "ax"
+
 /*
  * We use macros for low-level operations which need to be overridden
  * for paravirtualization.  The following will never clobber any registers:
@@ -788,7 +790,7 @@ ENDPROC(ptregs_clone)
  */
 .section .init.rodata,"a"
 ENTRY(interrupt)
-.text
+.section .entry.text, "ax"
 	.p2align 5
 	.p2align CONFIG_X86_L1_CACHE_SHIFT
 ENTRY(irq_entries_start)
@@ -807,7 +809,7 @@ vector=FIRST_EXTERNAL_VECTOR
       .endif
       .previous
 	.long 1b
-      .text
+      .section .entry.text, "ax"
 vector=vector+1
     .endif
   .endr
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 891268c..39f8d21 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -61,6 +61,8 @@
 #define __AUDIT_ARCH_LE	   0x40000000
 
 	.code64
+	.section .entry.text, "ax"
+
 #ifdef CONFIG_FUNCTION_TRACER
 #ifdef CONFIG_DYNAMIC_FTRACE
 ENTRY(mcount)
@@ -744,7 +746,7 @@ END(stub_rt_sigreturn)
  */
 	.section .init.rodata,"a"
 ENTRY(interrupt)
-	.text
+	.section .entry.text
 	.p2align 5
 	.p2align CONFIG_X86_L1_CACHE_SHIFT
 ENTRY(irq_entries_start)
@@ -763,7 +765,7 @@ vector=FIRST_EXTERNAL_VECTOR
       .endif
       .previous
 	.quad 1b
-      .text
+      .section .entry.text
 vector=vector+1
     .endif
   .endr
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index e70cc3d..459dce2 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -105,6 +105,7 @@ SECTIONS
 		SCHED_TEXT
 		LOCK_TEXT
 		KPROBES_TEXT
+		ENTRY_TEXT
 		IRQENTRY_TEXT
 		*(.fixup)
 		*(.gnu.warning)
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
index b3bfabc..c1a1216 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -11,6 +11,7 @@ extern char _sinittext[], _einittext[];
 extern char _end[];
 extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[];
 extern char __kprobes_text_start[], __kprobes_text_end[];
+extern char __entry_text_start[], __entry_text_end[];
 extern char __initdata_begin[], __initdata_end[];
 extern char __start_rodata[], __end_rodata[];
 
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index fe77e33..906c3ce 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -424,6 +424,12 @@
 		*(.kprobes.text)					\
 		VMLINUX_SYMBOL(__kprobes_text_end) = .;
 
+#define ENTRY_TEXT							\
+		ALIGN_FUNCTION();					\
+		VMLINUX_SYMBOL(__entry_text_start) = .;			\
+		*(.entry.text)						\
+		VMLINUX_SYMBOL(__entry_text_end) = .;
+
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 #define IRQENTRY_TEXT							\
 		ALIGN_FUNCTION();					\
-- 
1.7.1