On Sun, 2018-02-04 at 19:43 +0100, Thomas Gleixner wrote: > > __x86_return_thunk would look like this: > > __x86_return_thunk: > testl $0xf, PER_CPU_VAR(call_depth) > jnz 1f > stuff_rsb > 1: > decl PER_CPU_VAR(call_depth) > ret > > The call_depth variable would be reset on context switch.
Note that the 'jnz' can be predicted taken there, allowing the CPU to speculate all the way to the 'ret'... and beyond.
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