On 10/21/15 9:57 AM, Peter Zijlstra wrote:
In summary, your either-or logic doesn't hold in BPF world. A BPF >program can only access perf event in a highly restricted way. We >don't allow it calling perf_event_read_local() across core, so it >can't.
That's actually broken. My fault as well, since I didn't review that patch carefully enough. Will send a fix in a second. No matter what bpf program does that should never be a kernel splat.
Urgh, that's still horridly inconsistent. Can we please come up with a consistent interface to perf?
I had the same concerns during v1-v4 series of this set. My suggestion was to do ioctl(enable/disable) of events from userspace after receiving notification from kernel via my bpf_perf_event_output() helper. Wangnan's argument was that display refresh happens often and it's fast, so the time taken by user space to enable events on all cpus is too slow and ioctl does ipi and disturbs other cpus even more. So soft_disable done by the program to enable/disable particular events on all cpus kinda makes sense. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
