Messages in this thread | | | Date | Tue, 1 Oct 2019 20:52:44 -0400 | From | Joel Fernandes <> | Subject | Re: [PATCH v7 4/4] ftrace: Add an option for tracing console latencies |
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On Fri, Sep 20, 2019 at 05:22:19PM +0200, Viktor Rosendahl (BMW) wrote: > This new trace option "console-latency" will enable the latency > tracers to trace the console latencies. Previously this has always been > implicitely disabled. I guess this is because they are considered > to be well known and unavoidable. > > However, for some organizations it may nevertheless be desirable to > trace them. Basically, we want to be able to tell that there are > latencies in the system under test because someone has incorrectly > enabled the serial console. > > Signed-off-by: Viktor Rosendahl (BMW) <viktor.rosendahl@gmail.com> > --- > include/linux/irqflags.h | 22 ++++++++++++++++++++++ > kernel/printk/printk.c | 6 ++++-- > kernel/trace/trace.h | 1 + > kernel/trace/trace_irqsoff.c | 12 ++++++++++++ > 4 files changed, 39 insertions(+), 2 deletions(-) > > diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h > index 21619c92c377..3de891723331 100644 > --- a/include/linux/irqflags.h > +++ b/include/linux/irqflags.h > @@ -13,6 +13,7 @@ > #define _LINUX_TRACE_IRQFLAGS_H > > #include <linux/typecheck.h> > +#include <linux/types.h> > #include <asm/irqflags.h> > > /* Currently trace_softirqs_on/off is used only by lockdep */ > @@ -68,9 +69,30 @@ do { \ > defined(CONFIG_PREEMPT_TRACER) > extern void stop_critical_timings(void); > extern void start_critical_timings(void); > + extern bool console_tracing_disabled(void); > + > +# define console_stop_critical_timings(flag) \ > + do { \ > + typecheck(bool, flag); \ > + flag = console_tracing_disabled(); \ > + if (flag) \ > + stop_critical_timings(); \ > + } while (0) > + > +# define console_start_critical_timings(flag) \ > + do { \ > + typecheck(bool, flag); \ > + if (flag) \ > + start_critical_timings(); \ > + } while (0) > + > #else > # define stop_critical_timings() do { } while (0) > # define start_critical_timings() do { } while (0) > +# define console_stop_critical_timings(flag) \ > + do { typecheck(bool, flag); } while (0) > +# define console_start_critical_timings(flag) \ > + do { typecheck(bool, flag); } while (0) > #endif > > /* > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 1888f6a3b694..036460a7e4cd 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -2359,6 +2359,7 @@ void console_unlock(void) > static char ext_text[CONSOLE_EXT_LOG_MAX]; > static char text[LOG_LINE_MAX + PREFIX_MAX]; > unsigned long flags; > + bool cflag; > bool do_cond_resched, retry; > > if (console_suspended) { > @@ -2459,9 +2460,10 @@ void console_unlock(void) > */ > console_lock_spinning_enable(); > > - stop_critical_timings(); /* don't trace print latency */ > + /* don't trace print latency if it's disabled */ > + console_stop_critical_timings(cflag); > call_console_drivers(ext_text, ext_len, text, len); > - start_critical_timings(); > + console_start_critical_timings(cflag); > > if (console_lock_spinning_disable_and_check()) { > printk_safe_exit_irqrestore(flags); > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h > index 4913ed1138aa..93a8b82c27e4 100644 > --- a/kernel/trace/trace.h > +++ b/kernel/trace/trace.h > @@ -1262,6 +1262,7 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf, > C(PRINTK_MSGONLY, "printk-msg-only"), \ > C(CONTEXT_INFO, "context-info"), /* Print pid/cpu/time */ \ > C(LATENCY_FMT, "latency-format"), \ > + C(CONSOLE_LATENCY, "console-latency"), \ > C(RECORD_CMD, "record-cmd"), \ > C(RECORD_TGID, "record-tgid"), \ > C(OVERWRITE, "overwrite"), \ > diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c > index a745b0cee5d3..bc02be207a7a 100644 > --- a/kernel/trace/trace_irqsoff.c > +++ b/kernel/trace/trace_irqsoff.c > @@ -456,6 +456,18 @@ void stop_critical_timings(void) > EXPORT_SYMBOL_GPL(stop_critical_timings); > NOKPROBE_SYMBOL(stop_critical_timings); > > +bool console_tracing_disabled(void) > +{ > + struct trace_array *tr = irqsoff_trace; > + int pc = preempt_count(); > + > + if (!preempt_trace(pc) && !irq_trace()) > + return false;
Why this condition here? Why not just make the call to stop_critical_timings() dependent on the new flag you are adding? Please explain it more and add some comments.
thanks,
- Joel
> + > + return !(tr->trace_flags & TRACE_ITER_CONSOLE_LATENCY); > +} > +EXPORT_SYMBOL_GPL(console_tracing_disabled); > + > #ifdef CONFIG_FUNCTION_TRACER > static bool function_enabled; > > -- > 2.17.1 >
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