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GPUThread: Fix very rare or impossible FIFO corruption

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If the buffer wraps around once, and the GPU thread does not execute any
commands before the CPU thread reaches the end again, it could lose one
buffer's worth of commands.

Also don't keep incrementing the work count while this is happening.
Super unlikely unless a ton of data is being pushed through the FIFO.
This commit is contained in:
Stenzek 2025-07-24 21:05:41 +10:00
parent 13233cc82e
commit 22fb032f91
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1 changed files with 26 additions and 3 deletions
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29
src/core/gpu_thread.cpp
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@ -68,6 +68,7 @@ static u32 GetPendingCommandSize();
static void ResetCommandFIFO();
static bool IsCommandFIFOEmpty();
static void WakeGPUThread();
static void WakeGPUThreadIfSleeping();
static bool SleepGPUThread(bool allow_sleep);
static bool CreateDeviceOnThread(RenderAPI api, bool fullscreen, bool clear_fsui_state_on_failure, Error* error);
@ -168,12 +169,12 @@ GPUThreadCommand* GPUThread::AllocateCommand(GPUBackendCommandType command, u32
{
u32 read_ptr = s_state.command_fifo_read_ptr.load(std::memory_order_acquire);
u32 write_ptr = s_state.command_fifo_write_ptr.load(std::memory_order_relaxed);
if (read_ptr > write_ptr)
if (read_ptr > write_ptr) [[unlikely]]
{
u32 available_size = read_ptr - write_ptr;
while (available_size < (size + sizeof(GPUBackendCommandType)))
{
WakeGPUThread();
WakeGPUThreadIfSleeping();
read_ptr = s_state.command_fifo_read_ptr.load(std::memory_order_acquire);
available_size = (read_ptr > write_ptr) ? (read_ptr - write_ptr) : (COMMAND_QUEUE_SIZE - write_ptr);
}
@ -181,8 +182,19 @@ GPUThreadCommand* GPUThread::AllocateCommand(GPUBackendCommandType command, u32
else
{
const u32 available_size = COMMAND_QUEUE_SIZE - write_ptr;
if ((size + sizeof(GPUThreadCommand)) > available_size)
if ((size + sizeof(GPUThreadCommand)) > available_size) [[unlikely]]
{
// Can't wrap around until the video thread has at least started processing commands...
if (read_ptr == 0) [[unlikely]]
{
DEV_LOG("Buffer full and unprocessed, spinning");
do
{
WakeGPUThreadIfSleeping();
read_ptr = s_state.command_fifo_read_ptr.load(std::memory_order_acquire);
} while (read_ptr == 0);
}
// allocate a dummy command to wrap the buffer around
GPUThreadCommand* dummy_cmd = reinterpret_cast<GPUThreadCommand*>(&s_state.command_fifo_data[write_ptr]);
dummy_cmd->type = GPUBackendCommandType::Wraparound;
@ -295,6 +307,17 @@ void GPUThread::WakeGPUThread()
s_state.thread_wake_semaphore.Post();
}
ALWAYS_INLINE_RELEASE void GPUThread::WakeGPUThreadIfSleeping()
{
if (GetThreadWakeCount(s_state.thread_wake_count.load(std::memory_order_acquire)) < 0)
{
if (IsCommandFIFOEmpty())
return;
WakeGPUThread();
}
}
void GPUThread::SyncGPUThread(bool spin)
{
if (!s_state.use_gpu_thread)