Re: [PATCH RFC] rdma/ib: Add trace point macros to display human-readable values

Bart Van Assche
2017-11-01T15:59:47Z

On Wed, 2017-11-01 at 08:27 +0200, Leon Romanovsky wrote:
> Bart, Steve
>
> You attended the MS track, and for the rest of us, the quote below
> sounds a little bit cryptic. Does the quote below mean that Chuck's
> proposal is no-go?
>
> From LWN.net "Another attempt to address the tracepoint ABI problem" [1]
>
> "The solution that was arrived at for now, as related by Torvalds,
> is to hold off on adding explicit tracepoints to the kernel. Instead,
> support will be added to make it easy for an application to attach a
> BPF script to any function in the kernel, with access to that function's
> arguments."
>
> [1] https://lwn.net/Articles/737530/

What I remember is that Linus does not require us to avoid breaking user
space applications that use tracepoints. Powertop however is an exception
to this rule. Although it uses tracepoints, we must not break it. I also
remember that Linus noticed that the purpose of many tracepoints is to
allow users to trace a function and its arguments. Linus wants a better
approach for tracing kernel functions than adding an explicit tracepoint
to each kernel function. Maybe I wasn't listening carefully enough but I
haven't heard Linus saying that we would not be allowed to add new
tracepoints.

Bart.