Messages in this thread Patch in this message | | | Date | Mon, 28 Mar 2016 17:27:26 -0700 | From | Alexei Starovoitov <> | Subject | Re: [PATCH 1/4] perf core: Introduce new ioctl options to pause and resume ring buffer |
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On Mon, Mar 28, 2016 at 06:41:29AM +0000, Wang Nan wrote: > 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. > > Signed-off-by: Wang Nan <wangnan0@huawei.com> > Cc: He Kuang <hekuang@huawei.com> > Cc: Alexei Starovoitov <ast@kernel.org> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com> > Cc: Brendan Gregg <brendan.d.gregg@gmail.com> > Cc: Jiri Olsa <jolsa@kernel.org> > Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> > Cc: Namhyung Kim <namhyung@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Zefan Li <lizefan@huawei.com> > Cc: pi3orama@163.com > --- > 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 de24fbc..cb47da3 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -4341,6 +4341,19 @@ 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) {
should have been 'if (!rb)', right?
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