Merge branch 'fix-forgotten-futures-on-linux-lt-5.17' into 'master'

io: do not use IO_FORGOTTEN_FUTURES_SKIP_CQE on linux <= 5.17

See merge request !366

emper/Emper.cpp

@@ -141,6 +141,7 @@ void printInfo(std::ostream& strm) {
 }
 
 const bool IO_MUST_INVALIDATE_BROKEN_CHAIN = EMPER_LINUX_LT("5.15.0");
+const bool IO_FORGOTTEN_FUTURES_SKIP_CQE = EMPER_LINUX_GE("5.17");
 
 auto getFullVersion() -> std::string { return EMPER_FULL_VERSION; }
 

emper/Emper.hpp

@@ -212,6 +212,8 @@ const bool WAITFREE_IO_STEALING =
 // warnings during the comparison use not yet initialized components is reduced.
 extern const bool IO_MUST_INVALIDATE_BROKEN_CHAIN;
 
+extern const bool IO_FORGOTTEN_FUTURES_SKIP_CQE;
+
 enum class IoSqPoller {
 	off,
 	one,

emper/io/IoContext.cpp

@@ -81,8 +81,8 @@ auto IoContext::prepareFutureChain(Future &future, unsigned chain_length) -> uns
 	if (future.isForgotten()) {
 		// Do not generate cqes for forgotten futures this reduces the kernel
 		// and user space overhead for cqes we do not need in the first place.
-		// This has no effect on kernel versions not supporing IOSQE_CQE_SKIP_SUCCESS.
-		sqe->flags |= IOSQE_CQE_SKIP_SUCCESS;
+		// IOSQE_CQE_SKIP_SUCCESS is supported since Linux 5.17
+		if (IO_FORGOTTEN_FUTURES_SKIP_CQE) sqe->flags |= IOSQE_CQE_SKIP_SUCCESS;
 	}
 
 	// If we use a single io_uring and a SubmitActor the submission and preparation