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https://github.com/RGBCube/serenity
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UserspaceEmulator: Add a very simple instruction fetch cache
To avoid MMU region lookup on every single instruction fetch, we now cache a raw pointer to the current instruction. This gets automatically invalidated when we jump somewhere, but as long as we're executing sequentially, instruction fetches will hit the cache and bypass all the region lookup stuff. This is about a ~2x speedup. :^)
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8656835935
5 changed files with 44 additions and 4 deletions
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@ -61,23 +61,44 @@ void SoftCPU::dump() const
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printf("o=%u s=%u z=%u a=%u p=%u c=%u\n", of(), sf(), zf(), af(), pf(), cf());
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}
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void SoftCPU::update_code_cache()
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{
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auto* region = m_emulator.mmu().find_region({ cs(), eip() });
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ASSERT(region);
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m_cached_code_ptr = region->cacheable_ptr(eip() - region->base());
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m_cached_code_end = region->cacheable_ptr(region->size());
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}
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u8 SoftCPU::read8()
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{
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auto value = read_memory8({ cs(), eip() });
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if (!m_cached_code_ptr || m_cached_code_ptr >= m_cached_code_end)
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update_code_cache();
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u8 value = *m_cached_code_ptr;
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m_cached_code_ptr += 1;
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m_eip += 1;
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return value;
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}
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u16 SoftCPU::read16()
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{
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auto value = read_memory16({ cs(), eip() });
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if (!m_cached_code_ptr || (m_cached_code_ptr + 2) >= m_cached_code_end)
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update_code_cache();
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u16 value = *reinterpret_cast<const u16*>(m_cached_code_ptr);
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m_cached_code_ptr += 2;
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m_eip += 2;
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return value;
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}
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u32 SoftCPU::read32()
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{
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auto value = read_memory32({ cs(), eip() });
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if (!m_cached_code_ptr || (m_cached_code_ptr + 4) >= m_cached_code_end)
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update_code_cache();
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u32 value = *reinterpret_cast<const u32*>(m_cached_code_ptr);
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m_cached_code_ptr += 4;
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m_eip += 4;
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return value;
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}
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