On Mon, Jan 14, 2019 at 11:13:59PM +1100, Balbir Singh wrote: > On Fri, Jan 04, 2019 at 05:50:18PM +0000, Mark Rutland wrote: > > Hi Torsten, > > > > On Fri, Jan 04, 2019 at 03:10:53PM +0100, Torsten Duwe wrote: > > > Use -fpatchable-function-entry (gcc8) to add 2 NOPs at the beginning > > > of each function. Replace the first NOP thus generated with a quick LR > > > saver (move it to scratch reg x9), so the 2nd replacement insn, the call > > > to ftrace, does not clobber the value. Ftrace will then generate the > > > standard stack frames. > > Do we know what the overhead would be, if this was a link time change > for the first instruction? No, but it should be possible to benchamrk that for a given workload, which is what I'd like to see. > Also, I was under the impression that some arch's do ftrace_call_replace > under stop_machine(), is that a possibility here? Something like that is a possibility. I think we need numbers either way. Thanks, Mark.
