| Message ID | 20181204194044.9506-1-anders.roxell@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] tracing: add cond_resched to ftrace_replace_code() | expand |
On Tue, 4 Dec 2018 20:40:44 +0100 Anders Roxell <anders.roxell@linaro.org> 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(). This isn't urgent is it? That is, it doesn't need a stable tag? -- Steve
On Tue, 4 Dec 2018 at 23:33, Steven Rostedt <rostedt@goodmis.org> wrote: > > On Tue, 4 Dec 2018 20:40:44 +0100 > Anders Roxell <anders.roxell@linaro.org> 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(). > > This isn't urgent is it? No, it is not urgent. I'm trying to get allmodconfig to boot on arm64. > That is, it doesn't need a stable tag? Also I don't think its a regression, since clearly nobody has ever been able to boot an arm64 allmodconfig kernel or anything close to that. Cheers, Anders
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index c375e33239f7..7c9f49a5a1ab 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 call 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(); + do_for_each_ftrace_rec(pg, rec) { if (rec->flags & FTRACE_FL_DISABLED) @@ -2435,6 +2443,8 @@ void __weak ftrace_replace_code(int enable) /* Stop processing */ return; } + if (schedulable) + cond_resched(); } while_for_each_ftrace_rec(); }
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(+) -- 2.19.2