Re: [PATCH v2 net-next 1/3] perf, bpf: Add BPF support to all perf_event types

[Peter Zijlstra <peterz@infradead.org>]

On Tue, May 30, 2017 at 10:37:46AM -0700, Alexei Starovoitov wrote:
> On 5/30/17 9:51 AM, Peter Zijlstra wrote:

> > I'm not entirely sure I see how that is required. Should per task not
> > already work? The WARN that's there will only trigger if you call them
> > on the wrong task, which is something you shouldn't do anyway.
> 
> The kernel WARN is considered to be a bug of bpf infra. That's the
> reason we do all these checks at map update time and at run-time.
> The bpf program authors should be able to do all possible experiments
> until their scripts work. Dealing with kernel warns and reboots is not
> something user space folks like to do.
> Today bpf_perf_event_read() for per-task events isn't really
> working due to event->oncpu != cpu runtime check in there.
> If we convert warns to returns the existing scripts will continue
> to work as-is and per-task will be possible.

Ah yes.. I always forget that side of things (not ever having seen a
bpf thing working doesn't help either of course).

Let me consider that for a bit..