Received-SPF: pass (google.com: domain of linux-kernel+bounces-212018-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Message-ID: <47fad008a152957c87e9846fdbf40746b6e2871a.camel@linux.intel.com>
Subject: Re: [PATCH 1/8] perf/x86/uncore: Save the unit control address of
 all units
From: Tim Chen <tim.c.chen@linux.intel.com>
To: "Liang, Kan" <kan.liang@linux.intel.com>, peterz@infradead.org, 
	mingo@kernel.org, linux-kernel@vger.kernel.org
Cc: acme@kernel.org, namhyung@kernel.org, irogers@google.com,
 eranian@google.com,  ak@linux.intel.com, yunying.sun@intel.com
Date: Wed, 12 Jun 2024 10:33:05 -0700
In-Reply-To: <eb5d91d1-2898-45e0-a2d3-aa5c66155911@linux.intel.com>
References: <20240610201619.884021-1-kan.liang@linux.intel.com>
	 <20240610201619.884021-2-kan.liang@linux.intel.com>
	 <0f1ba5d8ecc62f774590077b2f88f5b64dd98452.camel@linux.intel.com>
	 <eb5d91d1-2898-45e0-a2d3-aa5c66155911@linux.intel.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.44.4 (3.44.4-3.fc36) 
Precedence: bulk
MIME-Version: 1.0

On Wed, 2024-06-12 at 10:49 -0400, Liang, Kan wrote:
>=20
>=20
> The id and pmu_idx+die can all be used as a key to search the RB tree in
> different places.
>=20
> The id is the physical ID of a unit. The search via id is invoked when
> adding a new unit. Perf needs to make sure that the same PMU idx
> (logical id) is assigned to the unit with the same physical ID. Because
> the units with the same physical ID in different dies share the same PMU.

This info about having same physical ID implies the same PMU
is worth mentioning in a comment and will be quite helpful in
understanding the rb-tree organization.

Thanks.

Tim
>=20
> The pmu_idx+die key is used when setting the cpumask. Please see
> intel_uncore_find_discovery_unit_id() in the patch 2. Perf wants to
> understand on which dies the given PMU is available.
>=20
> Since different keys can be used to search the RB tree, I think one of
> them has to traverse the whole tree. At the stage of adding a new unit,
> the tree is not complete yet. It minimizes the impact of the O(N)
> search. So I choose the pmu_idx+die rather than id.
>=20
> Also, the driver only does once to build the tree and set the cpumask at
> driver load time. I think the O(N) should be acceptable here.
>=20
> Thanks,
> Kan