/srv/irclogs.ubuntu.com/2017/08/22/#ubuntu-kernel.txt

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hwpplayer1Hi people16:37
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thgarniehi, I noticed that x86_64 ubuntu kernel configuration enables CONFIG_FUNCTION_TRACER on all SKUs. On x86_64 it hads a call on each function by default, do you know why it is enabled?17:39
thgarnie-hads +adds17:39
thgarnieWaste about 1.2% time in average on hackbench.17:44
keesogasawara, apw: ^^18:14
apwhwpplayer1: you trade off debugability against performance always18:15
apwit adds 4 or 5 noops to the top of an untraced function iirf18:16
apwiirc18:16
thgarnieno, not on x86_6418:16
thgarniethat's what the config says18:16
thgarniethe reality is a call __fentry__18:16
thgarnieNot sure if it is badly implemented on x86_64 (because you can do mnop-mcount) or because it is hard to do the nop swap.18:16
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thgarnieCorrection, the nop is added a runtime instead of using -mnop-mcount. Odd that it didn't happen when PIC is enabled then hum.18:49
thgarnieNot sure why I see a 1.2% average difference with/without function tracing on hackbench.18:50
hwpplayer1apw : it is not that easy19:14
jjohansensforshee: pull request sent to the ml21:51

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