Messages in this thread | | | Date | Wed, 5 Dec 2018 09:54:46 +0000 | From | Will Deacon <> | Subject | Re: [PATCH v2] tracing: add cond_resched to ftrace_replace_code() |
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Hi Anders, Steve,
On Tue, Dec 04, 2018 at 08:29:03PM +0100, Anders Roxell wrote: > When running in qemu on an kernel built with allmodconfig and debug > options (in particular kcov and ubsan) enabled, ftrace_replace_code > function call take minutes. The ftrace selftest calls > ftrace_replace_code to look >40000 through > ftrace_make_call/ftrace_make_nop, and these end up calling > __aarch64_insn_write/aarch64_insn_patch_text_nosync. > > Microseconds add up because this is called in a loop for each dyn_ftrace > record, and this triggers the softlockup watchdog unless we let it sleep > occasionally. > > Rework so that we call cond_resched() if !irqs_disabled() && !preempt_count(). > > Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org> > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > --- > kernel/trace/ftrace.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index c375e33239f7..7080eb464983 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -2419,11 +2419,19 @@ void __weak ftrace_replace_code(int enable) > { > struct dyn_ftrace *rec; > struct ftrace_page *pg; > + bool schedulable; > int failed; > > if (unlikely(ftrace_disabled)) > return; > > + /* > + * Some archs calls this function with interrupts or preemption > + * disabled. However, for other archs that can preempt, this can cause > + * an tremendous unneeded latency. > + */ > + schedulable = !irqs_disabled() && !preempt_count();
Is there a reason not to use preemptible() here?
Will
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