[PATCH 1/4] x86/cpufeature: Rework {boot_,}cpu_has()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
 xen/arch/x86/include/asm/cpufeature.h | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/include/asm/cpufeature.h 
b/xen/arch/x86/include/asm/cpufeature.h
index 4140ec0938b2..4f827cc6ff91 100644
--- a/xen/arch/x86/include/asm/cpufeature.h
+++ b/xen/arch/x86/include/asm/cpufeature.h
@@ -7,6 +7,7 @@
 #define __ASM_I386_CPUFEATURE_H
 
 #include <xen/const.h>
+#include <xen/stdbool.h>
 #include <asm/cpuid.h>
 
 #define cpufeat_word(idx)      ((idx) / 32)
@@ -17,7 +18,6 @@
 #define X86_FEATURE_ALWAYS      X86_FEATURE_LM
 
 #ifndef __ASSEMBLY__
-#include <xen/bitops.h>
 
 struct cpuinfo_x86 {
     unsigned char x86;                 /* CPU family */
@@ -43,8 +43,15 @@ 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

base-commit: 8f9c8274a4e3e860bd777269cb2c91971e9fa69e
prerequisite-patch-id: ceeba7d5ab9498cb188e5012953c7e8c9a86347d
prerequisite-patch-id: c0957b9e1157ae6eb8de973c96716fd02587c486
prerequisite-patch-id: d2574bba15748cd021e5b33fa50e6cadc38863b6
prerequisite-patch-id: 0f66cd4287ffdc06f24dc01c7d26fb428f3e8c09
prerequisite-patch-id: a585f61b546ff96be3624ff253f8100b2f465de6
prerequisite-patch-id: 54551cdefaca083b4a4b97528d27d0f3dc9753ee
prerequisite-patch-id: 051423463e4a34728ab524f03e801e7103777684
-- 
2.30.2