diff mbox series

[v2,07/10] x86/cpufeature: Rework {boot_,}cpu_has()

Message ID 20230524112526.3475200-8-andrew.cooper3@citrix.com (mailing list archive)
State New, archived
Headers show
Series x86: Introduce MSR_ARCH_CAPS into featuresets | expand

Commit Message

Andrew Cooper May 24, 2023, 11:25 a.m. UTC 
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>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>

v2:
 * Drop stdbool.  It is already covered by other includes.
---
 xen/arch/x86/include/asm/cpufeature.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)
diff mbox series

Patch

diff --git a/xen/arch/x86/include/asm/cpufeature.h b/xen/arch/x86/include/asm/cpufeature.h
index 4140ec0938b2..d0ead8e7a51e 100644
--- 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