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

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Date:   Tue, 23 May 2017 10:05:05 -0700
From:   Alexei Starovoitov <ast@...com>
To:     Peter Zijlstra <peterz@...radead.org>
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 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@...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);

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!