[16:37] <hwpplayer1> Hi people
[17:39] <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
[17:44] <thgarnie> Waste about 1.2% time in average on hackbench.
[18:14] <kees> ogasawara, apw: ^^
[18:15] <apw> hwpplayer1: you trade off debugability against performance always
[18:16] <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.
[18:49] <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.
[18:50] <thgarnie> Not sure why I see a 1.2% average difference with/without function tracing on hackbench.
[19:14] <hwpplayer1> apw : it is not that easy
[21:51] <jjohansen> sforshee: pull request sent to the ml