Em Fri, Feb 26, 2016 at 09:31:58AM +0000, Wang Nan escreveu: > Add new ioctl() to pause/resume ring-buffer output. > > In some situations we want to read from ring buffer only when we > ensure nothing can write to the ring buffer during reading. Without > this patch we have to turn off all events attached to this ring buffer > to achieve this. > > This patch is for supporting overwrite ring buffer. Following > commits will introduce new methods support reading from overwrite ring > buffer. Before reading caller must ensure the ring buffer is frozen, or > the reading is unreliable.
Peter, have you have the chance too look at this and the other kernel bits in this kit? - Arnaldo > Signed-off-by: Wang Nan <[email protected]> > Cc: He Kuang <[email protected]> > Cc: Alexei Starovoitov <[email protected]> > Cc: Arnaldo Carvalho de Melo <[email protected]> > Cc: Brendan Gregg <[email protected]> > Cc: Jiri Olsa <[email protected]> > Cc: Masami Hiramatsu <[email protected]> > Cc: Namhyung Kim <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Zefan Li <[email protected]> > Cc: [email protected] > --- > include/uapi/linux/perf_event.h | 1 + > kernel/events/core.c | 13 +++++++++++++ > kernel/events/internal.h | 11 +++++++++++ > kernel/events/ring_buffer.c | 7 ++++++- > 4 files changed, 31 insertions(+), 1 deletion(-) > > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > index 1afe962..a3c1903 100644 > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -401,6 +401,7 @@ struct perf_event_attr { > #define PERF_EVENT_IOC_SET_FILTER _IOW('$', 6, char *) > #define PERF_EVENT_IOC_ID _IOR('$', 7, __u64 *) > #define PERF_EVENT_IOC_SET_BPF _IOW('$', 8, __u32) > +#define PERF_EVENT_IOC_PAUSE_OUTPUT _IOW('$', 9, __u32) > > enum perf_event_ioc_flags { > PERF_IOC_FLAG_GROUP = 1U << 0, > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 94c47e3..a7075ae 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -4231,6 +4231,19 @@ static long _perf_ioctl(struct perf_event *event, > unsigned int cmd, unsigned lon > case PERF_EVENT_IOC_SET_BPF: > return perf_event_set_bpf_prog(event, arg); > > + case PERF_EVENT_IOC_PAUSE_OUTPUT: { > + struct ring_buffer *rb; > + > + rcu_read_lock(); > + rb = rcu_dereference(event->rb); > + if (!event->rb) { > + rcu_read_unlock(); > + return -EINVAL; > + } > + rb_toggle_paused(rb, !!arg); > + rcu_read_unlock(); > + return 0; > + } > default: > return -ENOTTY; > } > diff --git a/kernel/events/internal.h b/kernel/events/internal.h > index 2bbad9c..6a93d1b 100644 > --- a/kernel/events/internal.h > +++ b/kernel/events/internal.h > @@ -18,6 +18,7 @@ struct ring_buffer { > #endif > int nr_pages; /* nr of data pages */ > int overwrite; /* can overwrite itself > */ > + int paused; /* can write into ring > buffer */ > > atomic_t poll; /* POLL_ for wakeups */ > > @@ -65,6 +66,16 @@ static inline void rb_free_rcu(struct rcu_head *rcu_head) > rb_free(rb); > } > > +static inline void > +rb_toggle_paused(struct ring_buffer *rb, > + bool pause) > +{ > + if (!pause && rb->nr_pages) > + rb->paused = 0; > + else > + rb->paused = 1; > +} > + > extern struct ring_buffer * > rb_alloc(int nr_pages, long watermark, int cpu, int flags); > extern void perf_event_wakeup(struct perf_event *event); > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > index 1faad2c..22e1a47 100644 > --- a/kernel/events/ring_buffer.c > +++ b/kernel/events/ring_buffer.c > @@ -125,8 +125,11 @@ int perf_output_begin(struct perf_output_handle *handle, > if (unlikely(!rb)) > goto out; > > - if (unlikely(!rb->nr_pages)) > + if (unlikely(rb->paused)) { > + if (rb->nr_pages) > + local_inc(&rb->lost); > goto out; > + } > > handle->rb = rb; > handle->event = event; > @@ -244,6 +247,8 @@ ring_buffer_init(struct ring_buffer *rb, long watermark, > int flags) > INIT_LIST_HEAD(&rb->event_list); > spin_lock_init(&rb->event_lock); > init_irq_work(&rb->irq_work, rb_irq_work); > + > + rb->paused = rb->nr_pages ? 0 : 1; > } > > static void ring_buffer_put_async(struct ring_buffer *rb) > -- > 1.8.3.4
