Re: [PATCH v4 3/3] binder: add transaction latency tracer

Frankie Chang
2020-05-11T12:45:40Z

On Thu, 2020-05-07 at 10:55 +0200, Greg Kroah-Hartman wrote:
> On Thu, May 07, 2020 at 04:10:55PM +0800, Frankie Chang wrote:
> > From: "Frankie.Chang" <Frankie.Chang@mediatek.com>
> >
> > Record start/end timestamp for 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.
>
> Shouldn't that "printing" go to the trace buffer and not to the kernel
> information log?
>

Time limitation of recording is the reason why we don't just use trace
here.

In some long time stability test, such as MTBF,
the exception is caused by a series of transactions interaction.
Some abnormal transactions may be pending for a long time ago, they
could not be recorded due to buffer limited.

> >
> > /* Implement details */
> > - Add latency tracer module to monitor slow transaction.
> > The trace_binder_free_transaction would not be enabled
> > by default. Monitoring which transaction is too slow to
> > cause some of exceptions is important. So we hook the
> > tracepoint to call the monitor function.
> >
> > Signed-off-by: Frankie.Chang <Frankie.Chang@mediatek.com>
> > ---
> > drivers/android/Kconfig | 8 +++
> > drivers/android/Makefile | 1 +
> > drivers/android/binder.c | 2 +
> > drivers/android/binder_internal.h | 13 ++++
> > drivers/android/binder_latency_tracer.c | 105 +++++++++++++++++++++++++++++++
> > drivers/android/binder_trace.h | 26 +++++++-
> > 6 files changed, 152 insertions(+), 3 deletions(-)
> > create mode 100644 drivers/android/binder_latency_tracer.c
> >
> > Change from v4:
> > split up into patch series.
> >
> > Change from v3:
> > use tracepoints for binder_update_info and print_binder_transaction_ext,
> > instead of custom registration functions.
> >
> > Change from v2:
> > create transaction latency module to monitor slow transaction.
> >
> > Change from v1:
> > first patchset.
> >
> > 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/Makefile b/drivers/android/Makefile
> > index c9d3d0c9..552e8ac 100644
> > --- a/drivers/android/Makefile
> > +++ b/drivers/android/Makefile
> > @@ -4,3 +4,4 @@ ccflags-y += -I$(src) # needed for trace events
> > obj-$(CONFIG_ANDROID_BINDERFS) += binderfs.o
> > obj-$(CONFIG_ANDROID_BINDER_IPC) += binder.o binder_alloc.o
> > obj-$(CONFIG_ANDROID_BINDER_IPC_SELFTEST) += binder_alloc_selftest.o
> > +obj-$(CONFIG_BINDER_USER_TRACKING) += binder_latency_tracer.o
> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > index 4c3dd98..b89d75a 100644
> > --- a/drivers/android/binder.c
> > +++ b/drivers/android/binder.c
> > @@ -2657,6 +2657,7 @@ static void binder_transaction(struct binder_proc *proc,
> > return_error_line = __LINE__;
> > goto err_alloc_t_failed;
> > }
> > + trace_binder_update_info(t, e);
> > INIT_LIST_HEAD(&t->fd_fixups);
> > binder_stats_created(BINDER_STAT_TRANSACTION);
> > spin_lock_init(&t->lock);
> > @@ -5145,6 +5146,7 @@ static void print_binder_transaction_ilocked(struct seq_file *m,
> > t->to_thread ? t->to_thread->pid : 0,
> > t->code, t->flags, t->priority, t->need_reply);
> > spin_unlock(&t->lock);
> > + trace_print_binder_transaction_ext(m, t);
> >
> > if (proc != to_proc) {
> > /*
> > diff --git a/drivers/android/binder_internal.h b/drivers/android/binder_internal.h
> > index ed61b3e..24d7beb 100644
> > --- a/drivers/android/binder_internal.h
> > +++ b/drivers/android/binder_internal.h
> > @@ -12,6 +12,11 @@
> > #include <linux/types.h>
> > #include <linux/uidgid.h>
> >
> > +#ifdef CONFIG_BINDER_USER_TRACKING
> > +#include <linux/rtc.h>
> > +#include <linux/time.h>
> > +#endif
> > +
> > struct binder_context {
> > struct binder_node *binder_context_mgr_node;
> > struct mutex context_mgr_node_lock;
> > @@ -131,6 +136,10 @@ struct binder_transaction_log_entry {
> > uint32_t return_error;
> > uint32_t return_error_param;
> > char context_name[BINDERFS_MAX_NAME + 1];
> > +#ifdef CONFIG_BINDER_USER_TRACKING
> > + struct timespec timestamp;
> > + struct timeval tv;
> > +#endif
> > };
> >
> > struct binder_transaction_log {
> > @@ -520,6 +529,10 @@ struct binder_transaction {
> > * during thread teardown
> > */
> > spinlock_t lock;
> > +#ifdef CONFIG_BINDER_USER_TRACKING
> > + struct timespec timestamp;
> > + struct timeval tv;
> > +#endif
> > };
> >
> > /**
> > diff --git a/drivers/android/binder_latency_tracer.c b/drivers/android/binder_latency_tracer.c
> > new file mode 100644
> > index 0000000..45c14fb
> > --- /dev/null
> > +++ b/drivers/android/binder_latency_tracer.c
> > @@ -0,0 +1,105 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 MediaTek Inc.
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <uapi/linux/android/binder.h>
> > +#include "binder_alloc.h"
> > +#include "binder_internal.h"
> > +#include "binder_trace.h"
> > +
> > +/*
> > + * probe_binder_free_transaction - Output info of a delay transaction
> > + * @t: pointer to the over-time transaction
> > + */
> > +void probe_binder_free_transaction(void *ignore, 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;
>
> Why is 2 seconds somehow "magic" here?
>

Some of modules would trigger timeout NE if their binder transaction
don't finish in time, such as audio timeout (5 sec), even BT command
timeout (2 sec), etc.

Therefore, we want to record related transactions which exceed 2 sec. It
could be helpful to debug.

>
>
> > +
> > + 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);
>
> Why is the lock ok to give up here and not after the next call?
>

We would give up lock not here but after the next call, thanks for
reminding.

> > +
> > + 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));
> > +}
> > +
> > +static void probe_binder_update_info(void *ignore, struct binder_transaction *t,
> > + struct binder_transaction_log_entry *e)
> > +{
> > + ktime_get_ts(&e->timestamp);
> > + do_gettimeofday(&e->tv);
> > + e->tv.tv_sec -= (sys_tz.tz_minuteswest * 60);
> > + memcpy(&t->timestamp, &e->timestamp, sizeof(struct timespec));
> > + memcpy(&t->tv, &e->tv, sizeof(struct timeval));
>
> No locking needed?
>

We would add lock protection here, thanks a lot.