From: Alexei Starovoitov <ast@plumgrid.com>
To: Kaixu Xia <xiakaixu@huawei.com>,
davem@davemloft.net, acme@kernel.org, mingo@redhat.com,
a.p.zijlstra@chello.nl, masami.hiramatsu.pt@hitachi.com,
jolsa@kernel.org, daniel@iogearbox.net
Cc: wangnan0@huawei.com, linux-kernel@vger.kernel.org,
pi3orama@163.com, hekuang@huawei.com, netdev@vger.kernel.org
Subject: Re: [PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER
Date: Wed, 14 Oct 2015 14:28:55 -0700 [thread overview]
Message-ID: <561EC917.8090001@plumgrid.com> (raw)
In-Reply-To: <1444826277-94060-3-git-send-email-xiakaixu@huawei.com>
On 10/14/15 5:37 AM, Kaixu Xia wrote:
> + event->p_sample_disable = &enabler_event->sample_disable;
I don't like it as a concept and it's buggy implementation.
What happens here when enabler is alive, but other event is destroyed?
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -221,9 +221,12 @@ static u64 bpf_perf_event_sample_control(u64 r1, u64 index, u64 flag, u64 r4, u6
> struct bpf_array *array = container_of(map, struct bpf_array, map);
> struct perf_event *event;
>
> - if (unlikely(index >= array->map.max_entries))
> + if (unlikely(index > array->map.max_entries))
> return -E2BIG;
>
> + if (index == array->map.max_entries)
> + index = 0;
what is this hack for ?
Either use notification and user space disable or
call bpf_perf_event_sample_control() manually for each cpu.
next prev parent reply other threads:[~2015-10-14 21:29 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-14 12:37 [PATCH V2 0/2] bpf: enable/disable events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling Kaixu Xia
2015-10-14 12:37 ` [PATCH V2 1/2] bpf: control the trace data output on current cpu " Kaixu Xia
2015-10-14 13:49 ` [RFC PATCH] bpf: bpf_perf_event_sample_control_proto can be static kbuild test robot
2015-10-14 13:49 ` [PATCH V2 1/2] bpf: control the trace data output on current cpu when perf sampling kbuild test robot
2015-10-14 21:21 ` Alexei Starovoitov
2015-10-14 12:37 ` [PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER Kaixu Xia
2015-10-14 21:28 ` Alexei Starovoitov [this message]
2015-10-15 2:21 ` xiakaixu
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