Re: [PATCH v2] sched/debug: Add new tracepoint to track cpu_capacity

[Qais Yousef]

On 09/08/20 09:19, Phil Auld wrote:
> Hi Quais,
> 
> On Mon, Sep 07, 2020 at 12:02:24PM +0100 Qais Yousef wrote:
> > On 09/02/20 09:54, Phil Auld wrote:
> > > > 
> > > > I think this decoupling is not necessary. The natural place for those
> > > > scheduler trace_event based on trace_points extension files is
> > > > kernel/sched/ and here the internal sched.h can just be included.
> > > > 
> > > > If someone really wants to build this as an out-of-tree module there is
> > > > an easy way to make kernel/sched/sched.h visible.
> > > >
> > > 
> > > It's not so much that we really _want_ to do this in an external module.
> > > But we aren't adding more trace events and my (limited) knowledge of
> > > BPF let me to the conclusion that its raw tracepoint functionality
> > > requires full events.  I didn't see any other way to do it.
> > 
> > I did have a patch that allowed that. It might be worth trying to upstream it.
> > It just required a new macro which could be problematic.
> > 
> > https://github.com/qais-yousef/linux/commit/fb9fea29edb8af327e6b2bf3bc41469a8e66df8b
> > 
> > With the above I could attach using bpf::RAW_TRACEPOINT mechanism.
> >
> 
> Yeah, that could work. I meant there was no way to do it with what was there :)
> 
> In our initial attempts at using BPF to get at nr_running (which I was not
> involved in and don't have all the details...) there were issues being able to
> keep up and losing events.  That may have been an implementation issue, but
> using the module and trace-cmd doesn't have that problem. Hopefully you don't
> see that using RAW_TRACEPOINTs.

So I have a proper patch for that now, that actually turned out to be really
tiny once you untangle exactly what is missing.

Peter, bpf programs aren't considered ABIs AFAIK, do you have concerns about
that?

Thanks

--
Qais Yousef

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