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Merge pull request #3091 from Subv/hle_request_delat
Kernel/IPC: Add a small delay after each SyncRequest to prevent thread starvation.
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commit
2146311ad1
@ -67,13 +67,31 @@ ResultCode ServerSession::HandleSyncRequest(SharedPtr<Thread> thread) {
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// If this ServerSession has an associated HLE handler, forward the request to it.
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if (hle_handler != nullptr) {
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hle_handler->HandleSyncRequest(SharedPtr<ServerSession>(this));
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} else {
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}
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if (thread->status == THREADSTATUS_RUNNING) {
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// Put the thread to sleep until the server replies, it will be awoken in
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// svcReplyAndReceive.
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// svcReplyAndReceive for LLE servers.
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thread->status = THREADSTATUS_WAIT_IPC;
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// Add the thread to the list of threads that have issued a sync request with this
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// server.
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pending_requesting_threads.push_back(std::move(thread));
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if (hle_handler != nullptr) {
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// For HLE services, we put the request threads to sleep for a short duration to
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// simulate IPC overhead, but only if the HLE handler didn't put the thread to sleep for
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// other reasons like an async callback. The IPC overhead is needed to prevent
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// starvation when a thread only does sync requests to HLE services while a
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// lower-priority thread is waiting to run.
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// This delay was approximated in a homebrew application by measuring the average time
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// it takes for svcSendSyncRequest to return when performing the SetLcdForceBlack IPC
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// request to the GSP:GPU service in a n3DS with firmware 11.6. The measured values have
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// a high variance and vary between models.
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static constexpr u64 IPCDelayNanoseconds = 39000;
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thread->WakeAfterDelay(IPCDelayNanoseconds);
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} else {
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// Add the thread to the list of threads that have issued a sync request with this
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// server.
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pending_requesting_threads.push_back(std::move(thread));
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}
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}
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// If this ServerSession does not have an HLE implementation, just wake up the threads waiting
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