Messages in this thread | | | Date | Sat, 11 Sep 2021 23:28:32 +0800 | Subject | Re: [PATCH 2/2] scripts: ftrace - move the nop-processing in ftrace_init to compile time | From | Yinan Liu <> |
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This is my GCC version: GCC version 4.8.5 20150623 (red hat 4.8.5-44) (GCC) .
In fact, I see the make_nop processing in recordmcount. I'm still confused why this part can be directly replaced?
在 2021/9/11 下午10:12, Steven Rostedt 写道: > On Sat, 11 Sep 2021 21:50:43 +0800 > Yinan Liu <yinan@linux.alibaba.com> wrote: > >> When ftrace is enabled, ftrace_init will consume a period of >> time, usually around 15~20ms. Approximately 60% of the time is >> consumed by nop-processing. Moving the nop-processing to the >> compile time can speed up the kernel boot process. >> >> performance test: >> env: Intel(R) Xeon(R) CPU E5-2682 v4 @ 2.50GHz >> method: before and after patching, compare the >> total time of ftrace_init(), and verify >> the functionality of ftrace. >> >> avg_time of ftrace_init: >> with patch: 7.114ms >> without patch: 15.763ms > What compiler are you using? Because by default, gcc should already do > this for you. In fact, recordmcount isn't even called with the latest > gcc, as gcc creates mcount_loc and inserts nops. > > This was implemented before, but because we use to have "ideal nops" > that was determined at run time, because the different CPUs had > different efficiency on what nop was used, we had to do it at run time. > But that is no longer the case today, so we can revisit this. > >> Signed-off-by: Yinan Liu <yinan@linux.alibaba.com> >> --- >> kernel/trace/ftrace.c | 4 ++++ >> scripts/recordmcount.h | 14 ++++++++++++++ >> 2 files changed, 18 insertions(+) >> >> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c >> index c236da868990..ae3fba331179 100644 >> --- a/kernel/trace/ftrace.c >> +++ b/kernel/trace/ftrace.c >> @@ -6261,6 +6261,10 @@ static int ftrace_process_locs(struct module *mod, >> * until we are finished with it, and there's no >> * reason to cause large interrupt latencies while we do it. >> */ >> +#if defined CONFIG_X86 || defined CONFIG_X86_64 || defined CONFIG_ARM || defined CONFIG_ARM64 > We don't list archs in generic files. The above needs to be something like: > > #ifdef ARCH_HAS_MCOUNT_NOP > > or some name like that, and then that macro gets defined by the arch > header (include/asm/ftrace.h) > > > >> + ret = 0; >> + goto out; >> +#endif > space should be here. > >> if (!mod) >> local_irq_save(flags); >> ftrace_update_code(mod, start_pg); > -- Steve
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