Re: [PATCH tip 0/9] tracing: attach eBPF programs to tracepoints/syscalls/kprobe

[Steven Rostedt]

On Wed, 21 Jan 2015 17:49:08 -0800
Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:


> > This also makes it keeping events in the soft-disabled state.
> 
> I was never able to figure out the use case for soft-disabled state.
> Probably historical before static_key was done.

No, it's not historical at all. The "soft-disable" is a way to enable
from any context. You can't enable a static key from NMI or interrupt
context, but you can enable a "soft-disable" there.

As you can enable or disable events from any function that the function
tracer may trace, I needed a way to enable them (make the tracepoint
active), but do nothing until something else turns them on.

-- Steve

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