netdev - Re: [PATCH net-next 1/2] perf, bpf: add support for HW

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Message-ID: <20170523163134.saalqlizp5opc5tz@hirez.programming.kicks-ass.net>
Date:   Tue, 23 May 2017 18:31:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <ast@...com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Brendan Gregg <bgregg@...flix.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Teng Qin <qinteng@...com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH net-next 1/2] perf, bpf: add support for HW_CACHE and RAW
 events

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@...com>
> > > 
> > > 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);
 
 	if (event->tp_event->prog)
 		return -EEXIST;