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Date: Wed, 21 Jan 2015 20:56:43 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Alexei Starovoitov <ast@plumgrid.com>
Cc: Namhyung Kim <namhyung@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Jiri Olsa <jolsa@redhat.com>, "David S. Miller" <davem@davemloft.net>,
        Daniel Borkmann <dborkman@redhat.com>,
        Hannes Frederic Sowa <hannes@stressinduktion.org>,
        Brendan Gregg <brendan.d.gregg@gmail.com>,
        Linux API <linux-api@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH tip 0/9] tracing: attach eBPF programs to
 tracepoints/syscalls/kprobe
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On Wed, 21 Jan 2015 17:49:08 -0800
Alexei Starovoitov <ast@plumgrid.com> 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