Re: [PATCH net-next 1/2] perf, bpf: add support for HW_CACHE and RAW events

[Alexei Starovoitov]

On 5/23/17 9:31 AM, Peter Zijlstra wrote:
> On Tue, May 23, 2017 at 07:38:08AM -0700, Alexei Starovoitov wrote:
> > On 5/23/17 12:42 AM, Peter Zijlstra wrote:
> > > On Mon, May 22, 2017 at 03:48:39PM -0700, Alexei Starovoitov wrote:
> > > > From: Teng Qin <qinteng@xxxxxx>
> > > >
> > > > This commit adds support for attach BPF program to RAW and HW_CACHE type
> > > > events, and support for read HW_CACHE type event counters in BPF
> > > > program. Existing code logic already supports them, so this commit is
> > > > just update Enum value checks.
> > >
> > > So what I'm missing is why they were not supported previously, and what
> > > changed to allow it now.
> >
> > that code path simply wasn't tested previously. Nothing changed on
> > bpf side and on perf side.
> > Why it wasn't added on day one? There was no demand. Now people
> > use bpf more and more and few folks got confused that these types
> > of perf events were not supported, hence we're adding it.
>
> OK. Is there anything stopping people from wanting to use the dynamic
> types, as found in:
>
>   /sys/bus/event_source/devices/*/type
>
> ?
>
> In which case, do we want something like this instead?
>
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 971f7259108f..4aa5f3011cf8 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8063,12 +8063,8 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
>  	bool is_kprobe, is_tracepoint;
>  	struct bpf_prog *prog;
>
> -	if (event->attr.type == PERF_TYPE_HARDWARE ||
> -	    event->attr.type == PERF_TYPE_SOFTWARE)
> -		return perf_event_set_bpf_handler(event, prog_fd);
> -
>  	if (event->attr.type != PERF_TYPE_TRACEPOINT)
> -		return -EINVAL;
> +		return perf_event_set_bpf_handler(event, prog_fd);

Good point. We were actually looking at how to deal with msr and cstate
events. That should indeed address it.
Will respin.
Thanks for the feedback!