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Kernel: Remove s_processor_lock by making s_processors statically sized

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Currently in SMP mode we hard code support for up to only 8 processors.
There is no reason for this to be a dynamic allocation that needs to be
guarded by a spinlock. Instead use a Array<T* with inline storage of 8,
allowing each processor to initialize it self in place, avoiding all
the need for locks.
This commit is contained in:
Brian Gianforcaro 2021-05-18 01:49:34 -07:00 committed by Andreas Kling
parent 1415b2cfc3
commit 7540f4268b
Notes: sideshowbarker 2024-07-18 17:43:53 +09:00 
Author: https://github.com/bgianfo
Commit: https://github.com/SerenityOS/serenity/commit/7540f4268b9
Pull-request: https://github.com/SerenityOS/serenity/pull/7243
Reviewed-by: https://github.com/awesomekling
2 changed files with 15 additions and 14 deletions
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16
Kernel/Arch/i386/CPU.cpp
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@ -924,15 +924,13 @@ UNMAP_AFTER_INIT void write_xcr0(u64 value)
READONLY_AFTER_INIT FPUState Processor::s_clean_fpu_state;
READONLY_AFTER_INIT static Vector<Processor*>* s_processors;
static SpinLock s_processor_lock;
READONLY_AFTER_INIT static ProcessorContainer s_processors {};
READONLY_AFTER_INIT volatile u32 Processor::g_total_processors;
static volatile bool s_smp_enabled;
Vector<Processor*>& Processor::processors()
ProcessorContainer& Processor::processors()
{
VERIFY(s_processors);
return *s_processors;
return s_processors;
}
Processor& Processor::by_id(u32 cpu)
@ -1239,13 +1237,9 @@ UNMAP_AFTER_INIT void Processor::initialize(u32 cpu)
m_info = new ProcessorInfo(*this);
{
ScopedSpinLock lock(s_processor_lock);
// We need to prevent races between APs starting up at the same time
if (!s_processors)
s_processors = new Vector<Processor*>();
if (cpu >= s_processors->size())
s_processors->resize(cpu + 1);
(*s_processors)[cpu] = this;
VERIFY(cpu < s_processors.size());
s_processors[cpu] = this;
}
}

13
Kernel/Arch/x86/CPU.h
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@ -623,6 +623,11 @@ struct DeferredCallEntry {
bool was_allocated;
};
class Processor;
// Note: We only support processors at most at the moment,
// so allocate 8 slots of inline capacity in the container.
using ProcessorContainer = Array<Processor*, 8>;
class Processor {
friend class ProcessorInfo;
@ -665,7 +670,7 @@ class Processor {
void gdt_init();
void write_raw_gdt_entry(u16 selector, u32 low, u32 high);
void write_gdt_entry(u16 selector, Descriptor& descriptor);
static Vector<Processor*>& processors();
static ProcessorContainer& processors();
static void smp_return_to_pool(ProcessorMessage& msg);
static ProcessorMessage& smp_get_from_pool();
@ -751,8 +756,10 @@ public:
{
auto& procs = processors();
size_t count = procs.size();
for (size_t i = 0; i < count; i++)
callback(*procs[i]);
for (size_t i = 0; i < count; i++) {
if (procs[i] != nullptr)
callback(*procs[i]);
}
return IterationDecision::Continue;
}