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Date: Tue, 5 Nov 2024 13:24:23 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Chun-Tse Shao <ctshao@google.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Namhyung Kim <namhyung@kernel.org>,
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	Adrian Hunter <adrian.hunter@intel.com>, Liang@google.com,
	Kan <kan.liang@linux.intel.com>, Ze Gao <zegao2021@gmail.com>,
	Yang Jihong <yangjihong1@huawei.com>,
	Weilin Wang <weilin.wang@intel.com>,
	linux-perf-users@vger.kernel.org
Subject: Re: [PATCH 2/3] perf: Reveal PMU type in fdinfo
Message-ID: <20241105122423.GJ24862@noisy.programming.kicks-ass.net>
References: <20241031223948.4179222-1-ctshao@google.com>
 <20241031223948.4179222-2-ctshao@google.com>
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In-Reply-To: <20241031223948.4179222-2-ctshao@google.com>

On Thu, Oct 31, 2024 at 10:39:44PM +0000, Chun-Tse Shao wrote:
> It gives useful info on knowing which PMUs are reserved by this process.
> Also add extra attributes which would be useful.
> 
> ```
> Testing cycles
> $ ./perf stat -e cycles &
> $ cat /proc/`pidof perf`/fdinfo/3
> pos:    0
> flags:  02000002
> mnt_id: 16
> ino:    3081
> perf_event-orig_type:   0
> perf_event-attr.config1:        0
> perf_event-attr.config2:        0
> perf_event-attr.config3:        0
> 
> Testing L1-dcache-load-misses//
> $ ./perf stat -e L1-dcache-load-misses &
> $ cat /proc/`pidof perf`/fdinfo/3
> pos:    0
> flags:  02000002
> mnt_id: 16
> ino:    1072
> perf_event-attr.type:   3
> perf_event-attr.config: 65536
> perf_event-attr.config1:        0
> perf_event-attr.config2:        0
> perf_event-attr.config3:        0
> ```

First time I hear about fdinfo.. How much of an ABI is this, and why
this random selection of the perf_event_attr structure? What if someone
else wants something and then we change it. Will this then break ABI?