Messages in this thread | ![/](/images/icornerl.gif) | | From | Christophe Leroy <> | Subject | Re: [RFC PATCH 6/9] powerpc/ftrace: Update and move function profile instructions out-of-line | Date | Thu, 21 Dec 2023 15:20:14 +0000 |
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Le 21/12/2023 à 15:25, Steven Rostedt a écrit : > On Thu, 21 Dec 2023 10:46:08 +0000 > Christophe Leroy <christophe.leroy@csgroup.eu> wrote: > >>> To enable ftrace, the nop at function entry is changed to an >>> unconditional branch to 'tramp'. The call to ftrace_caller() may be >>> updated to ftrace_regs_caller() depending on the registered ftrace ops. >>> On 64-bit powerpc, we additionally change the instruction at 'tramp' to >>> 'mflr r0' from an unconditional branch back to func+4. This is so that >>> functions entered through the GEP can skip the function profile sequence >>> unless ftrace is enabled. >>> >>> With the context_switch microbenchmark on a P9 machine, there is a >>> performance improvement of ~6% with this patch applied, going from 650k >>> context switches to 690k context switches without ftrace enabled. With >>> ftrace enabled, the performance was similar at 86k context switches. >> >> Wondering how significant that context_switch micorbenchmark is. >> >> I ran it on both mpc885 and mpc8321 and I'm a bit puzzled by some of the >> results: >> # ./context_switch --no-fp >> Using threads with yield on cpus 0/0 touching FP:no altivec:no vector:no >> vdso:no >> >> On 885, I get the following results before and after your patch. >> >> CONFIG_FTRACE not selected : 44,9k >> CONFIG_FTRACE selected, before : 32,8k >> CONFIG_FTRACE selected, after : 33,6k >> >> All this is with CONFIG_INIT_STACK_ALL_ZERO which is the default. But >> when I select CONFIG_INIT_STACK_NONE, the CONFIG_FTRACE not selected >> result is only 34,4. >> >> On 8321: >> >> CONFIG_FTRACE not selected : 100,3k >> CONFIG_FTRACE selected, before : 72,5k >> CONFIG_FTRACE selected, after : 116k >> >> So the results look odd to me. > > > BTW, CONFIG_FTRACE just enables the tracing system (I would like to change > that to CONFIG_TRACING, but not sure if I can without breaking .configs all > over the place). > > The nops for ftrace is enabled with CONFIG_FUNCTION_TRACER.
Yes I selected both CONFIG_FTRACE and CONFIG_FUNCTION_TRACER
Christophe
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