From f7f9fe3b65940932fb2e1bb9faacea992b69b54d Mon Sep 17 00:00:00 2001
From: Florian Schmaus <flow@cs.fau.de>
Date: Fri, 3 Jun 2022 15:43:58 +0200
Subject: [PATCH] [ContextManager] Remove the put/get free context cycle
The put/get free context cycle in ContextManager::start() (if
continuation stealing is enabled) became unnecessary with
c66551bfbafb ("[Context] Use 'jmp' instead of 'ret' to kickoff the
context").
---
emper/ContextManager.cpp | 27 ++++-----------------------
1 file changed, 4 insertions(+), 23 deletions(-)
diff --git a/emper/ContextManager.cpp b/emper/ContextManager.cpp
index 3f4cb54d..92afe0bb 100644
--- a/emper/ContextManager.cpp
+++ b/emper/ContextManager.cpp
@@ -72,34 +72,15 @@ void ContextManager::start() {
return;
}
+ Context* freeContext = nullptr;
if constexpr (emper::CONTINUATION_STEALING) {
Fibril::tryResumeFibril(fibrilResumeValue);
- // The code below only needs to be executed if we did a long jmp
- // before. But optimizing for it is not worth it. If we longjmp
- // and can not resume the Fibril and we where not on the initial
- // context of the Fibril, then we need to take care to recycle the
- // context.
- Context* currentContext = Context::getCurrentContext();
- if (currentContext) {
- // If we would simply call currentContext->start() here, then we
- // would jump to an invalid address. The reason is that as soon as
- // the Context::kickoff() is executed, the alpha function address,
- // which was just popped of the stack, will be potentially
- // overriden by a stack push operation. And such operations are
- // very likely. Instead we simply free the current context here,
- // so that it is re-initialized later on.
-
- // TODO: Adjust the assembly to not use 'ret' to reach the
- // kickoff function, but instead jmp. This would not destroy the
- // kickoff's function pointer on the stack, and we could call
- // currentContext->start() here. This would print a small
- // performance gain.
- putFreeContext(currentContext);
- }
+ freeContext = Context::getCurrentContext();
}
- Context* freeContext = getFreeContext();
+ if (!freeContext) freeContext = getFreeContext();
+
freeContext->start();
}
--
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