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kern: devirtualize KAutoObject::DynamicCast<>()

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This is an optimization that saves the most common type of virtual call in the kernel (DynamicCast)
by storing class token as a member, rather than getting it via virtual call every time.

This does not currently cost any memory space on 64-bit targets, due to pre-existing padding space.

This optimization can be turned off via a compile-time flag for accuracy.
This commit is contained in:
Michael Scire 2021-10-16 16:24:06 -07:00
parent 26c02e2019
commit bfffe6b119
3 changed files with 40 additions and 4 deletions
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7
libraries/libmesosphere/include/mesosphere/kern_build_config.hpp
View file

@ -32,3 +32,10 @@
//#define MESOSPHERE_BUILD_FOR_TRACING
#define MESOSPHERE_ENABLE_PANIC_REGISTER_DUMP
#define MESOSPHERE_ENABLE_HARDWARE_SINGLE_STEP
/* NOTE: This enables fast class token storage using a class member. */
/* This saves a virtual call when doing KAutoObject->DynCast<>(), */
/* at the cost of storing class tokens inside the class object. */
/* However, as of (10/16/2021) KAutoObject has an unused class member */
/* of the right side, and so this does not actually cost any space. */
#define MESOSPHERE_ENABLE_DEVIRTUALIZED_DYNAMIC_CAST

32
libraries/libmesosphere/include/mesosphere/kern_k_auto_object.hpp
View file

@ -63,7 +63,11 @@ namespace ams::kern {
}
constexpr ALWAYS_INLINE bool IsDerivedFrom(const TypeObj &rhs) {
return (this->GetClassToken() | rhs.GetClassToken()) == this->GetClassToken();
return IsClassTokenDerivedFrom(this->GetClassToken(), rhs.GetClassToken());
}
static constexpr ALWAYS_INLINE bool IsClassTokenDerivedFrom(ClassTokenType derived, ClassTokenType base) {
return (derived | base) == derived;
}
};
private:
@ -71,11 +75,23 @@ namespace ams::kern {
private:
KAutoObject *m_next_closed_object;
std::atomic<u32> m_ref_count;
#if defined(MESOSPHERE_ENABLE_DEVIRTUALIZED_DYNAMIC_CAST)
ClassTokenType m_class_token;
#else
u32 m_reserved;
#endif
public:
static KAutoObject *Create(KAutoObject *ptr);
public:
constexpr ALWAYS_INLINE explicit KAutoObject() : m_next_closed_object(nullptr), m_ref_count(0), m_reserved(0) { MESOSPHERE_ASSERT_THIS(); }
constexpr ALWAYS_INLINE explicit KAutoObject() : m_next_closed_object(nullptr), m_ref_count(0),
#if defined(MESOSPHERE_ENABLE_DEVIRTUALIZED_DYNAMIC_CAST)
m_class_token(0)
#else
m_reserved(0)
#endif
{
MESOSPHERE_ASSERT_THIS();
}
/* Destroy is responsible for destroying the auto object's resources when ref_count hits zero. */
virtual void Destroy() { MESOSPHERE_ASSERT_THIS(); }
@ -90,11 +106,19 @@ namespace ams::kern {
}
ALWAYS_INLINE bool IsDerivedFrom(const TypeObj &rhs) const {
return this->GetTypeObj().IsDerivedFrom(rhs);
#if defined(MESOSPHERE_ENABLE_DEVIRTUALIZED_DYNAMIC_CAST)
return TypeObj::IsClassTokenDerivedFrom(m_class_token, rhs.GetClassToken());
#else
return this->GetTypeObj().IsDerivedFrom(rhs);
#endif
}
ALWAYS_INLINE bool IsDerivedFrom(const KAutoObject &rhs) const {
return this->IsDerivedFrom(rhs.GetTypeObj());
#if defined(MESOSPHERE_ENABLE_DEVIRTUALIZED_DYNAMIC_CAST)
return TypeObj::IsClassTokenDerivedFrom(m_class_token, rhs.m_class_token);
#else
return this->IsDerivedFrom(rhs.GetTypeObj());
#endif
}
template<typename Derived>

5
libraries/libmesosphere/source/kern_k_auto_object.cpp
View file

@ -19,6 +19,11 @@ namespace ams::kern {
KAutoObject *KAutoObject::Create(KAutoObject *obj) {
obj->m_ref_count = 1;
#if defined(MESOSPHERE_ENABLE_DEVIRTUALIZED_DYNAMIC_CAST)
obj->m_class_token = obj->GetTypeObj().GetClassToken();
#endif
return obj;
}