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Date: Tue, 14 Jan 2025 11:30:15 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: kan.liang@linux.intel.com
Cc: mingo@redhat.com, acme@kernel.org, namhyung@kernel.org,
	irogers@google.com, adrian.hunter@intel.com,
	linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
	ak@linux.intel.com, eranian@google.com, dapeng1.mi@linux.intel.com
Subject: Re: [PATCH V8 2/2] perf/x86/intel: Support PEBS counters snapshotting
Message-ID: <20250114103015.GN5388@noisy.programming.kicks-ass.net>
References: <20250106142103.1735729-1-kan.liang@linux.intel.com>
 <20250106142103.1735729-2-kan.liang@linux.intel.com>
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In-Reply-To: <20250106142103.1735729-2-kan.liang@linux.intel.com>

On Mon, Jan 06, 2025 at 06:21:03AM -0800, kan.liang@linux.intel.com wrote:

> The current Linux perf sample read feature intends to read the counters
> of other member events when the leader event is overflowing.

This doesn't sound right. Any event in the group that has 'read_format &
FORMAT_GROUP' will read the entire group. There is absolutely nothing
leader specific here. Nor sampling for that matter, read() also works.

You can have 3 sampling events, all with FORMAT_GROUP on, with a
non-sampling leader.

Anyway, let me go read the code...