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Date: Wed, 21 Oct 2015 14:06:36 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Alexei Starovoitov <ast@plumgrid.com>
Cc: "David S. Miller" <davem@davemloft.net>, Ingo Molnar <mingo@kernel.org>,
        Wang Nan <wangnan0@huawei.com>, He Kuang <hekuang@huawei.com>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Daniel Borkmann <daniel@iogearbox.net>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 2/3] bpf: introduce bpf_perf_event_output()
 helper
Message-ID: <20151021120636.GB3604@twins.programming.kicks-ass.net>
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On Tue, Oct 20, 2015 at 08:02:34PM -0700, Alexei Starovoitov wrote:
> This helper is used to send raw data from eBPF program into
> special PERF_TYPE_SOFTWARE/PERF_COUNT_SW_BPF_OUTPUT perf_event.
> User space needs to perf_event_open() it (either for one or all cpus) and
> store FD into perf_event_array (similar to bpf_perf_event_read() helper)
> before eBPF program can send data into it.
> 

> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 2881145cda86..d3c417615361 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -110,6 +110,7 @@ enum perf_sw_ids {
>  	PERF_COUNT_SW_ALIGNMENT_FAULTS		= 7,
>  	PERF_COUNT_SW_EMULATION_FAULTS		= 8,
>  	PERF_COUNT_SW_DUMMY			= 9,
> +	PERF_COUNT_SW_BPF_OUTPUT		= 10,
>  
>  	PERF_COUNT_SW_MAX,			/* non-ABI */
>  };

Do you really need the new type? Can't you use DUMMY for this?