x86/cpufeature: Rework {boot_,}cpu_has()

One area where Xen deviates from Linux is that test_bit() forces a volatile
read.  This leads to poor code generation, because the optimiser cannot merge
bit operations on the same word.

Drop the use of test_bit(), and write the expressions in regular C.  This
removes the include of bitops.h (which is a frequent source of header
tangles), and it offers the optimiser far more flexibility.

Bloat-o-meter reports a net change of:

  add/remove: 0/0 grow/shrink: 21/87 up/down: 641/-2751 (-2110)

with half of that in x86_emulate() alone.  vmx_ctxt_switch_to() seems to be
the fastpath with the greatest delta at -24, where the optimiser has
successfully removed the branch hidden in cpu_has_msr_tsc_aux.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/include/asm/cpufeature.h b/xen/arch/x86/include/asm/cpufeature.h
index 4140ec0938b2091686a85e4d777645673cd81758..d0ead8e7a51e151b79bb76ab8f2ef902ee04c676 100644 (file)
--- a/xen/arch/x86/include/asm/cpufeature.h
+++ b/xen/arch/x86/include/asm/cpufeature.h
@@ -17,7 +17,6 @@
 #define X86_FEATURE_ALWAYS      X86_FEATURE_LM
 
 #ifndef __ASSEMBLY__
-#include <xen/bitops.h>
 
 struct cpuinfo_x86 {
     unsigned char x86;                 /* CPU family */
@@ -43,8 +42,15 @@ struct cpuinfo_x86 {
 
 extern struct cpuinfo_x86 boot_cpu_data;
 
-#define cpu_has(c, bit)                test_bit(bit, (c)->x86_capability)
-#define boot_cpu_has(bit)      test_bit(bit, boot_cpu_data.x86_capability)
+static inline bool cpu_has(const struct cpuinfo_x86 *info, unsigned int feat)
+{
+    return info->x86_capability[cpufeat_word(feat)] & cpufeat_mask(feat);
+}
+
+static inline bool boot_cpu_has(unsigned int feat)
+{
+    return cpu_has(&boot_cpu_data, feat);
+}
 
 #define CPUID_PM_LEAF                    6
 #define CPUID6_ECX_APERFMPERF_CAPABILITY 0x1