Performance tweaks in core/timer.lua #337
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
The definition of call_timers() in core/timer.lua is moved out of run_to_time() to avoid generation of the non-compileable bytecode UCLO (bytecode 51 in the current version of LuaJIT). Wrapping the call to ffi.C.get_time_ns() in run() with tonumber() avoids the allocation of a cdata object that is difficult for the sink optimizer to remove.
lukego
added a commit
that referenced
this pull request
Dec 10, 2014
Performance tweaks in core/timer.lua
|
Great analysis!! |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The definition of call_timers() in core/timer.lua is moved out of
run_to_time() to avoid generation of the non-compileable bytecode
UCLO (bytecode 51 in the current version of LuaJIT).
Wrapping the call to ffi.C.get_time_ns() in run() with tonumber()
avoids the allocation of a cdata object that is difficult for the sink
optimizer to remove. Here is the IR of a typical trace without tonumber():
0036 > p32 UREFC timer.lua:22 #0
0037 > udt ULOAD 0036
0038 > p32 EQ 0037 [0x4123cfa0]
0039 r15 u64 CALLXS 0x408c78
0040 rax > cdt CNEWI +12 0039
0041 > fun EQ 0035 timer.lua:37
The allocation of the uint64_t cdata object (CNEWI +12) at 0040 is not sunk. With tonumber():
0050 > p32 UREFC timer.lua:22 #0
0051 > udt ULOAD 0050
0052 > p32 EQ 0051 [0x40465fa0]
0053 rax u64 CALLXS 0x408c78
0054 {sink} cdt CNEWI +12 0053
0055 > fun EQ 0049 tonumber
0056 xmm7 num CONV 0053 num.u64
0057 > fun EQ 0035 timer.lua:37
The allocation at 0054 is trivially sunk due to tonumber() acting directly on the return value of the call to get_time_ns().