From c16200ac024d20c974d164e2d0b5e6622a4d4d79 Mon Sep 17 00:00:00 2001
From: Bartosz Taudul <wolf.pld@gmail.com>
Date: Wed, 12 Aug 2020 14:01:02 +0200
Subject: [PATCH] Add ring buffer for perf events.

---
 client/TracyRingBuffer.hpp | 105 +++++++++++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 client/TracyRingBuffer.hpp

diff --git a/client/TracyRingBuffer.hpp b/client/TracyRingBuffer.hpp
new file mode 100644
index 00000000..c1415485
--- /dev/null
+++ b/client/TracyRingBuffer.hpp
@@ -0,0 +1,105 @@
+namespace tracy
+{
+
+class RingBuffer
+{
+public:
+    RingBuffer( uint32_t size, int fd )
+        : m_size( size )
+        , m_fd( fd )
+    {
+        const auto pageSize = uint32_t( getpagesize() );
+        assert( size >= pageSize );
+        assert( __builtin_popcount( size ) == 1 );
+        m_mapSize = size + pageSize;
+        m_mapAddr = mmap( nullptr, m_mapSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0 );
+        if( !m_mapAddr )
+        {
+            m_fd = 0;
+            close( fd );
+            return;
+        }
+        m_metadata = (perf_event_mmap_page*)m_mapAddr;
+        assert( m_metadata->data_offset == pageSize );
+        m_buffer = ((char*)m_mapAddr) + pageSize;
+    }
+
+    ~RingBuffer()
+    {
+        if( m_mapAddr ) munmap( m_mapAddr, m_mapSize );
+        if( m_fd ) close( m_fd );
+    }
+
+    RingBuffer( const RingBuffer& ) = delete;
+    RingBuffer& operator=( const RingBuffer& ) = delete;
+
+    RingBuffer( RingBuffer&& other )
+    {
+        memcpy( (char*)&other, (char*)this, sizeof( RingBuffer ) );
+        m_mapAddr = nullptr;
+        m_fd = 0;
+    }
+
+    RingBuffer& operator=( RingBuffer&& other )
+    {
+        memcpy( (char*)&other, (char*)this, sizeof( RingBuffer ) );
+        m_mapAddr = nullptr;
+        m_fd = 0;
+        return *this;
+    }
+
+    bool IsValid() const { return m_mapAddr != nullptr; }
+
+    void Enable()
+    {
+        ioctl( m_fd, PERF_EVENT_IOC_ENABLE, 0 );
+    }
+
+    bool HasData() const
+    {
+        const auto head = LoadHead();
+        return head > m_metadata->data_tail;
+    }
+
+    void Read( void* dst, uint64_t offset, uint64_t cnt )
+    {
+        auto src = ( m_metadata->data_tail + offset ) % m_size;
+        if( src + cnt <= m_size )
+        {
+            memcpy( dst, m_buffer + src, cnt );
+        }
+        else
+        {
+            const auto s0 = m_size - src;
+            memcpy( dst, m_buffer + src, s0 );
+            memcpy( (char*)dst + s0, m_buffer, cnt - s0 );
+        }
+    }
+
+    void Advance( uint64_t cnt )
+    {
+        StoreTail( m_metadata->data_tail + cnt );
+    }
+
+private:
+    uint64_t LoadHead() const
+    {
+        return std::atomic_load_explicit( (const volatile std::atomic<uint64_t>*)&m_metadata->data_head, std::memory_order_acquire );
+    }
+
+    void StoreTail( uint64_t tail )
+    {
+        std::atomic_store_explicit( (volatile std::atomic<uint64_t>*)&m_metadata->data_tail, tail, std::memory_order_release );
+    }
+
+    size_t m_size;
+    size_t m_mapSize;
+    void* m_mapAddr;
+
+    perf_event_mmap_page* m_metadata;
+    char* m_buffer;
+
+    int m_fd;
+};
+
+}