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hwpplayer1 | Hi people | 16:37 |
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thgarnie | hi, 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 +adds | 17:39 |
thgarnie | Waste about 1.2% time in average on hackbench. | 17:44 |
kees | ogasawara, apw: ^^ | 18:14 |
apw | hwpplayer1: you trade off debugability against performance always | 18:15 |
apw | it adds 4 or 5 noops to the top of an untraced function iirf | 18:16 |
apw | iirc | 18:16 |
thgarnie | no, not on x86_64 | 18:16 |
thgarnie | that's what the config says | 18:16 |
thgarnie | the reality is a call __fentry__ | 18:16 |
thgarnie | Not 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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thgarnie | Correction, 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 |
thgarnie | Not sure why I see a 1.2% average difference with/without function tracing on hackbench. | 18:50 |
hwpplayer1 | apw : it is not that easy | 19:14 |
jjohansen | sforshee: pull request sent to the ml | 21:51 |
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