[patch 3/3] x86/process: Optimize TIF_NOTSC switch

[Thomas Gleixner]

Provide and use a toggle helper instead of doing it with a branch.

x86_64:
3662       8505      16   12183    2f97 Before
3646       8505      16   12167    2f87 After 

i386:
5906       9388    1804   17098    42ca Before
5834       9324    1740   16898    4202 After

Signed-off-by: Thomas Gleixner <t...@linutronix.de>
---
 arch/x86/include/asm/tlbflush.h |   10 ++++++++++
 arch/x86/kernel/process.c       |   22 ++++------------------
 2 files changed, 14 insertions(+), 18 deletions(-)

--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -110,6 +110,16 @@ static inline void cr4_clear_bits(unsign
        }
 }
 
+static inline void cr4_toggle_bits(unsigned long mask)
+{
+       unsigned long cr4;
+
+       cr4 = this_cpu_read(cpu_tlbstate.cr4);
+       cr4 ^= mask;
+       this_cpu_write(cpu_tlbstate.cr4, cr4);
+       __write_cr4(cr4);
+}
+
 /* Read the CR4 shadow. */
 static inline unsigned long cr4_read_shadow(void)
 {
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -116,11 +116,6 @@ void flush_thread(void)
        fpu__clear(&tsk->thread.fpu);
 }
 
-static void hard_disable_TSC(void)
-{
-       cr4_set_bits(X86_CR4_TSD);
-}
-
 void disable_TSC(void)
 {
        preempt_disable();
@@ -129,15 +124,10 @@ void disable_TSC(void)
                 * Must flip the CPU state synchronously with
                 * TIF_NOTSC in the current running context.
                 */
-               hard_disable_TSC();
+               cr4_set_bits(X86_CR4_TSD);
        preempt_enable();
 }
 
-static void hard_enable_TSC(void)
-{
-       cr4_clear_bits(X86_CR4_TSD);
-}
-
 static void enable_TSC(void)
 {
        preempt_disable();
@@ -146,7 +136,7 @@ static void enable_TSC(void)
                 * Must flip the CPU state synchronously with
                 * TIF_NOTSC in the current running context.
                 */
-               hard_enable_TSC();
+               cr4_clear_bits(X86_CR4_TSD);
        preempt_enable();
 }
 
@@ -212,12 +202,8 @@ void __switch_to_xtra(struct task_struct
        if ((tifp ^ tifn) & _TIF_BLOCKSTEP)
                toggle_debugctlmsr(DEBUGCTLMSR_BTF);
 
-       if ((tifp ^ tifn) & _TIF_NOTSC) {
-               if (tifn & _TIF_NOTSC)
-                       hard_disable_TSC();
-               else
-                       hard_enable_TSC();
-       }
+       if ((tifp ^ tifn) & _TIF_NOTSC)
+               cr4_toggle_bits(X86_CR4_TSD);
 }
 
 /*