[PATCH] x86/cpuid: Fewer CPUID invocations in init_scattered_cpuid_features()

From: David Woodhouse
Date: Tue Jan 23 2018 - 09:54:40 EST


We were doing a fresh CPUID for every single bit in every single output
register. Do it once and then harvest *all* the bits we want.

We were also doing the max_level check with a new CPUID invocation for
every single bit. Stop that too.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
Spotted this in my travels; it offended me.

arch/x86/kernel/cpu/scattered.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index df11f5d..26c15fb 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -23,8 +23,8 @@ static const struct cpuid_bit cpuid_bits[] = {
{ X86_FEATURE_EPB, CPUID_ECX, 3, 0x00000006, 0 },
{ X86_FEATURE_CAT_L3, CPUID_EBX, 1, 0x00000010, 0 },
{ X86_FEATURE_CAT_L2, CPUID_EBX, 2, 0x00000010, 0 },
- { X86_FEATURE_CDP_L3, CPUID_ECX, 2, 0x00000010, 1 },
{ X86_FEATURE_MBA, CPUID_EBX, 3, 0x00000010, 0 },
+ { X86_FEATURE_CDP_L3, CPUID_ECX, 2, 0x00000010, 1 },
{ X86_FEATURE_HW_PSTATE, CPUID_EDX, 7, 0x80000007, 0 },
{ X86_FEATURE_CPB, CPUID_EDX, 9, 0x80000007, 0 },
{ X86_FEATURE_PROC_FEEDBACK, CPUID_EDX, 11, 0x80000007, 0 },
@@ -38,20 +38,35 @@ void init_scattered_cpuid_features(struct cpuinfo_x86 *c)
u32 regs[4];
const struct cpuid_bit *cb;

+ /* Max level for basic CPUID leaves */
+ max_level = cpuid_eax(0);
+
for (cb = cpuid_bits; cb->feature; cb++) {

+ /* Are we on to extended CPUID leaves yet? */
+ if (cb->level >= 0x80000000 && max_level < 0x80000000) {
+ max_level = cpuid_eax(0x80000000);
+ if (max_level < 0x80000000 || max_level > 0x8000ffff) {
+ /* No extended leaves are supported */
+ break;
+ }
+ }
+
/* Verify that the level is valid */
- max_level = cpuid_eax(cb->level & 0xffff0000);
- if (max_level < cb->level ||
- max_level > (cb->level | 0xffff))
+ if (cb->level > max_level)
continue;

cpuid_count(cb->level, cb->sub_leaf, &regs[CPUID_EAX],
&regs[CPUID_EBX], &regs[CPUID_ECX],
&regs[CPUID_EDX]);

- if (regs[cb->reg] & (1 << cb->bit))
- set_cpu_cap(c, cb->feature);
+ do {
+ if (regs[cb->reg] & (1 << cb->bit))
+ set_cpu_cap(c, cb->feature);
+
+ } while (cb[1].level == cb[0].level &&
+ cb[1].sub_leaf == cb[0].sub_leaf &&
+ cb++);
}
}

--
2.7.4