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GGitHub[ctxprof] Handle instrumenting functions with musttail calls (#135121)

e7aed23d创建于 2025年4月15日历史提交

文件	最后提交记录	最后更新时间
tests	[ctxprof] Handle instrumenting functions with musttail calls (#135121) Functions with musttail calls can't be roots because we can't instrument their ret to release the context. This patch tags their CtxRoot field in their FunctionData. In compiler-rt we then know not to allow such functions become roots, and also not confuse CtxRoot == 0x1 with there being a context root. Currently we also lose the context tree under such cases. We can, in a subsequent patch, have the root detector search past these functions.	1 年前
CMakeLists.txt	[ctxprof] root autodetection mechanism (#133147) This is an optional mechanism that automatically detects roots. It's a best-effort mechanism, and its main goal is to *avoid* pointing at the message pump function as a root. This is the function that polls message queue(s) in an infinite loop, and is thus a bad root (it never exits). High-level, when collection is requested - which should happen when a server has already been set up and handing requests - we spend a bit of time sampling all the server's threads. Each sample is a stack which we insert in a PerThreadCallsiteTrie. After a while, we run for each PerThreadCallsiteTrie the root detection logic. We then traverse all the FunctionData, find the ones matching the detected roots, and allocate a ContextRoot for them. From here, we special case FunctionData objects, in __llvm_ctx_profile_get_context, that have a CtxRoot and route them to __llvm_ctx_profile_start_context. For this to work, on the llvm side, we need to have all functions call __llvm_ctx_profile_release_context because they _might_ be roots. This comes at a slight (percentages) penalty during collection - which we can afford since the overall technique is ~5x faster than normal instrumentation. We can later explore conditionally enabling autoroot detection and avoiding this penalty, if desired. Note that functions that musttail call` can't have their return instrumented this way, and a subsequent patch will harden the mechanism against this case. The mechanism could be used in combination with explicit root specification, too.	1 年前
CtxInstrContextNode.h	[ctxprof] Handle instrumenting functions with musttail calls (#135121) Functions with musttail calls can't be roots because we can't instrument their ret to release the context. This patch tags their CtxRoot field in their FunctionData. In compiler-rt we then know not to allow such functions become roots, and also not confuse CtxRoot == 0x1 with there being a context root. Currently we also lose the context tree under such cases. We can, in a subsequent patch, have the root detector search past these functions.	1 年前
CtxInstrProfiling.cpp	[ctxprof] Handle instrumenting functions with musttail calls (#135121) Functions with musttail calls can't be roots because we can't instrument their ret to release the context. This patch tags their CtxRoot field in their FunctionData. In compiler-rt we then know not to allow such functions become roots, and also not confuse CtxRoot == 0x1 with there being a context root. Currently we also lose the context tree under such cases. We can, in a subsequent patch, have the root detector search past these functions.	1 年前
CtxInstrProfiling.h	[ctxprof] Handle instrumenting functions with musttail calls (#135121) Functions with musttail calls can't be roots because we can't instrument their ret to release the context. This patch tags their CtxRoot field in their FunctionData. In compiler-rt we then know not to allow such functions become roots, and also not confuse CtxRoot == 0x1 with there being a context root. Currently we also lose the context tree under such cases. We can, in a subsequent patch, have the root detector search past these functions.	1 年前
RootAutoDetector.cpp	[ctxprof] Handle instrumenting functions with musttail calls (#135121) Functions with musttail calls can't be roots because we can't instrument their ret to release the context. This patch tags their CtxRoot field in their FunctionData. In compiler-rt we then know not to allow such functions become roots, and also not confuse CtxRoot == 0x1 with there being a context root. Currently we also lose the context tree under such cases. We can, in a subsequent patch, have the root detector search past these functions.	1 年前
RootAutoDetector.h	[ctxprof] root autodetection mechanism (#133147) This is an optional mechanism that automatically detects roots. It's a best-effort mechanism, and its main goal is to *avoid* pointing at the message pump function as a root. This is the function that polls message queue(s) in an infinite loop, and is thus a bad root (it never exits). High-level, when collection is requested - which should happen when a server has already been set up and handing requests - we spend a bit of time sampling all the server's threads. Each sample is a stack which we insert in a PerThreadCallsiteTrie. After a while, we run for each PerThreadCallsiteTrie the root detection logic. We then traverse all the FunctionData, find the ones matching the detected roots, and allocate a ContextRoot for them. From here, we special case FunctionData objects, in __llvm_ctx_profile_get_context, that have a CtxRoot and route them to __llvm_ctx_profile_start_context. For this to work, on the llvm side, we need to have all functions call __llvm_ctx_profile_release_context because they _might_ be roots. This comes at a slight (percentages) penalty during collection - which we can afford since the overall technique is ~5x faster than normal instrumentation. We can later explore conditionally enabling autoroot detection and avoiding this penalty, if desired. Note that functions that musttail call` can't have their return instrumented this way, and a subsequent patch will harden the mechanism against this case. The mechanism could be used in combination with explicit root specification, too.	1 年前