Messages in this thread | | | Date | Wed, 4 Sep 2019 11:46:26 -0400 | From | Joel Fernandes <> | Subject | Re: [PATCH 2/2] sched/debug: add sched_update_nr_running tracepoint |
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On Wed, Sep 04, 2019 at 03:57:59PM +0100, Qais Yousef wrote: > On 09/04/19 10:41, Joel Fernandes wrote: > > On Wed, Sep 04, 2019 at 03:20:17PM +0100, Qais Yousef wrote: > > > On 09/04/19 09:06, Joel Fernandes wrote: > > > > > > > > > > It is actually true. > > > > > > > > > > But you need to make the distinction between a tracepoint > > > > > and a trace event first. > > > > > > > > I know this distinction well. > > > > > > > > > What Valentin is talking about here is the *bare* > > > > > tracepoint without any event associated with them like the one I added to the > > > > > scheduler recently. These ones are not accessible via eBPF, unless something > > > > > has changed since I last tried. > > > > > > > > Can this tracepoint be registered on with tracepoint_probe_register()? > > > > Quickly looking at these new tracepoint, they can be otherwise how would they > > > > even work right? If so, then eBPF can very well access it. Look at > > > > __bpf_probe_register() and bpf_raw_tracepoint_open() which implement the > > > > BPF_RAW_TRACEPOINT_OPEN. > > > > > > Humm okay. I tried to use raw tracepoint with bcc but failed to attach. But > > > maybe I missed something on the way it should be used. AFAICT it was missing > > > the bits that I implemented in [1]. Maybe the method you mention is lower level > > > than bcc. > > > > Oh, Ok. Not sure about BCC. I know that facebook folks are using *existing* > > tracepoints (not trace events) to probe context switches and such (probably > > not through BCC but some other BPF tracing code). Peter had rejected trace > > events they were trying to add IIRC, so they added BPF_RAW_TRACEPOINT_OPEN > > then IIRC. > > Looking at the history BPF_RAW_TRACEPOINT_OPEN was added with the support for > RAW_TRACEPOINT c4f6699dfcb8 (bpf: introduce BPF_RAW_TRACEPOINT). > > Anyway, if you ever get a chance please try it and let me know. I might have > done something wrong and you're more of a eBPF guru than I am :-)
eBPF guru and me? no way ;-) I have tried out BPF_RAW_TRACEPOINT_OPEN before and it works as expected. Are there not any in-kernel samples? Perhaps Alexei can post some if there are not.
thanks,
- Joel
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