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Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get the selected hardware PMU conuter

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发自我的 iPhone

> 在 2015年7月17日，下午8:45，Peter Zijlstra <peterz@infradead.org> 写道：
> 
>> On Fri, Jul 17, 2015 at 08:27:43PM +0800, Wangnan (F) wrote:
>> I think we can check the limitation in BPF program.
> 
> You typically do not want to rely on your program for correctness.

Sorry. NOT BPF program. What I want to express is bpf_read_pmu() function which is called from BPF program. User can put anything into the map during preparation but he or she gets only error code if the perf event he or she read from doesn't meet our restriction at runtime.

>> What about this:
>> 
>> event must on current CPU or must be on current process. If not,
>> bpf_read_pmu() should simply return an error.
> 
> OK, that's workable. That enforces the constraints outside of the
> program itself.
> 
>> With current design it is easy to implement, and users can still control
>> it through bpf map.
>> 
>> But what if we really want cross-cpu PMU accessing? Impossible?
> 
> Under the assumption that the eBPF program is called from tracing, and
> therefore from any context (task, softirq, irq and nmi), yes impossible.
> 
> You cannot do (synchronous) IPIs from either IRQ context or with IRQs
> disabled. And both are valid trace contexts.

What about software perf event? For example, tracepoints?

Thank you.
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[RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get the selected hardware PMU conuter kaixu xia <xiakaixu@huawei.com> - 2015-07-17 12:50 +0200
  Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 13:10 +0200
    Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 13:40 +0200
    Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 13:40 +0200
      Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 13:50 +0200
        Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 14:00 +0200
          Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 14:00 +0200
            Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 14:10 +0200
              Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 14:10 +0200
              Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 14:20 +0200
                Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 14:40 +0200
                Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 14:50 +0200
                Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 14:50 +0200
                Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get the selected hardware PMU conuter pi3orama <pi3orama@163.com> - 2015-07-17 15:10 +0200
                Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter Peter Zijlstra <peterz@infradead.org> - 2015-07-17 15:30 +0200
                Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get the selected hardware PMU conuter pi3orama <pi3orama@163.com> - 2015-07-17 15:50 +0200
    Re: [RFC PATCH 5/6] bpf: Implement function bpf_read_pmu() that get  the selected hardware PMU conuter "Wangnan (F)" <wangnan0@huawei.com> - 2015-07-17 13:40 +0200

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