engine: Separate JIT traces for each app callback #1242
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Create an execution barrier that a JIT trace cannot cross. During recording, the current trace must end when it reaches a barrier and then a new root trace starts immediately afterwards. This is implemented as a simple "nop" C library function. The existing "trace stitching" mechanism provides the required semantics i.e. stop current trace, call nop function, start new trace with linkage.
eugeneia
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# Conflicts: # src/core/app.lua
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Early feedback seems to be that this change does not introduce problems, but it remains to be seen how effective it really is for simplifying performance diagnostics. I will see if it helps to resolve #1239 before really proposing it for merge. |
lukego
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This branch makes the engine ensure that JIT traces never cross between the engine and app callbacks. This is intended both to make JIT trace dumps more readable (don't mix engine and apps in the same trace) and to limit the impact of issues like JIT blacklistings (prevent problems in one app from propagating into other apps or the engine.)
This is achieved using a new primitive function
jit.tracebarrier()that JIT traces cannot cross. During recording, a call tojit.tracebarrier()will immediately finish the current trace and then start a new root trace. This appears as a "trace stitch" in the log.This branch makes the engine execute such a trace barrier immediately before and after each call to an app.
Performance impact needs to be evaluated. See also raptorjit/raptorjit#115.