Re: [PATCH v1 1/1] binder: transaction latency tracking for user build

[Joel Fernandes <joel@joelfernandes.org>]

On Wed, Feb 05, 2020 at 09:36:12AM +0000, Greg Kroah-Hartman wrote:
> On Wed, Feb 05, 2020 at 02:52:52PM +0800, Frankie Chang wrote:
> > Record start/end timestamp to binder transaction.
> > When transaction is completed or transaction is free,
> > it would be checked if transaction latency over threshold (2 sec),
> > if yes, printing related information for tracing.
> > 
> > Signed-off-by: Frankie Chang <Frankie.Chang@mediatek.com>
> > ---
> >  drivers/android/Kconfig           |    8 +++
> >  drivers/android/binder.c          |  107 +++++++++++++++++++++++++++++++++++++
> >  drivers/android/binder_internal.h |    4 ++
> >  3 files changed, 119 insertions(+)
> > 
> > diff --git a/drivers/android/Kconfig b/drivers/android/Kconfig
> > index 6fdf2ab..7ba80eb 100644
> > --- a/drivers/android/Kconfig
> > +++ b/drivers/android/Kconfig
> > @@ -54,6 +54,14 @@ config ANDROID_BINDER_IPC_SELFTEST
> >  	  exhaustively with combinations of various buffer sizes and
> >  	  alignments.
> >  
> > +config BINDER_USER_TRACKING
> > +	bool "Android Binder transaction tracking"
> > +	help
> > +	  Used for track abnormal binder transaction which is over 2 seconds,
> > +	  when the transaction is done or be free, this transaction would be
> > +	  checked whether it executed overtime.
> > +	  If yes, printing out the detail info about it.
> > +
> >  endif # if ANDROID
> >  
> >  endmenu
> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > index e9bc9fc..5a352ee 100644
> > --- a/drivers/android/binder.c
> > +++ b/drivers/android/binder.c
> > @@ -76,6 +76,11 @@
> >  #include "binder_internal.h"
> >  #include "binder_trace.h"
> >  
> > +#ifdef CONFIG_BINDER_USER_TRACKING
> > +#include <linux/rtc.h>
> > +#include <linux/time.h>
> > +#endif
> > +
> >  static HLIST_HEAD(binder_deferred_list);
> >  static DEFINE_MUTEX(binder_deferred_lock);
> >  
> > @@ -591,8 +596,104 @@ struct binder_transaction {
> >  	 * during thread teardown
> >  	 */
> >  	spinlock_t lock;
> > +#ifdef CONFIG_BINDER_USER_TRACKING
> > +	struct timespec timestamp;
> > +	struct timeval tv;
> > +#endif
> >  };
> >  
> > +#ifdef CONFIG_BINDER_USER_TRACKING
> > +
> > +/*
> > + * binder_print_delay - Output info of a delay transaction
> > + * @t:          pointer to the over-time transaction
> > + */
> > +static void binder_print_delay(struct binder_transaction *t)
> > +{
> > +	struct rtc_time tm;
> > +	struct timespec *startime;
> > +	struct timespec cur, sub_t;
> > +
> > +	ktime_get_ts(&cur);
> > +	startime = &t->timestamp;
> > +	sub_t = timespec_sub(cur, *startime);
> > +
> > +	/* if transaction time is over than 2 sec,
> > +	 * show timeout warning log.
> > +	 */
> > +	if (sub_t.tv_sec < 2)
> > +		return;
> > +
> > +	rtc_time_to_tm(t->tv.tv_sec, &tm);
> > +
> > +	spin_lock(&t->lock);
> > +	pr_info_ratelimited("%d: from %d:%d to %d:%d",
> > +			    t->debug_id,
> > +			    t->from ? t->from->proc->pid : 0,
> > +			    t->from ? t->from->pid : 0,
> > +			    t->to_proc ? t->to_proc->pid : 0,
> > +			    t->to_thread ? t->to_thread->pid : 0);
> > +	spin_unlock(&t->lock);
> > +
> > +	pr_info_ratelimited(" total %u.%03ld s code %u start %lu.%03ld android %d-%02d-%02d %02d:%02d:%02d.%03lu\n",
> > +			    (unsigned int)sub_t.tv_sec,
> > +			    (sub_t.tv_nsec / NSEC_PER_MSEC),
> > +			    t->code,
> > +			    (unsigned long)startime->tv_sec,
> > +			    (startime->tv_nsec / NSEC_PER_MSEC),
> > +			    (tm.tm_year + 1900), (tm.tm_mon + 1), tm.tm_mday,
> > +			    tm.tm_hour, tm.tm_min, tm.tm_sec,
> > +			    (unsigned long)(t->tv.tv_usec / USEC_PER_MSEC));
> > +}
> 
> Ick, why not use a tracepoint for this instead?
> 
> And what is userspace supposed to do with this if they see it?

Or another option is to implement this separately outside of binder.c using
register_trace_* on the existing binder tracepoints, similar to what say the
block tracer or preempt-off tracers do. Call it, say, "binder-latency tracer".

That way all of this tracing code is in-kernel but outside of binder.c.

thanks,

 - Joel