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Tue, 31 Aug 2021 08:58:25 +0000 From: "nakamura.shun@fujitsu.com" To: Rob Herring CC: "peterz@infradead.org" , "mingo@redhat.com" , "acme@kernel.org" , "mark.rutland@arm.com" , "alexander.shishkin@linux.intel.com" , "jolsa@redhat.com" , "namhyung@kernel.org" , "linux-kernel@vger.kernel.org" , "linux-perf-users@vger.kernel.org" Subject: Re: [PATCH 1/3] libperf: Add processing to scale the counters obtained during the read() system call when multiplexing Thread-Topic: [PATCH 1/3] libperf: Add processing to scale the counters obtained during the read() system call when multiplexing Thread-Index: AQHXmFsxBFGvQYUD8Uu1pPLYL2hYdauCbgJwgArtTKA= Date: Tue, 31 Aug 2021 08:58:25 +0000 Message-ID: References: <20210820093908.734503-1-nakamura.shun@fujitsu.com> <20210820093908.734503-2-nakamura.shun@fujitsu.com> In-Reply-To: Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_a7295cc1-d279-42ac-ab4d-3b0f4fece050_Enabled=True;MSIP_Label_a7295cc1-d279-42ac-ab4d-3b0f4fece050_SiteId=a19f121d-81e1-4858-a9d8-736e267fd4c7;MSIP_Label_a7295cc1-d279-42ac-ab4d-3b0f4fece050_SetDate=2021-08-31T08:58:24.835Z;MSIP_Label_a7295cc1-d279-42ac-ab4d-3b0f4fece050_Name=FUJITSU-RESTRICTED;MSIP_Label_a7295cc1-d279-42ac-ab4d-3b0f4fece050_ContentBits=0;MSIP_Label_a7295cc1-d279-42ac-ab4d-3b0f4fece050_Method=Standard; 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charset="iso-2022-jp" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: fujitsu.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: OSBPR01MB4600.jpnprd01.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6ab42369-c7de-4fdc-6f58-08d96c5d7e35 X-MS-Exchange-CrossTenant-originalarrivaltime: 31 Aug 2021 08:58:25.3855 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: a19f121d-81e1-4858-a9d8-736e267fd4c7 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: wya/LpRTX84zTtPfzVhJsTOmICqF+WZjz5hO561euyZ4JqLeUEv6scHHaqHK/GWgINacDwp3E3Nf8C2kR5UrClf+F8pC90ag1iTYariypcg= X-MS-Exchange-Transport-CrossTenantHeadersStamped: OSAPR01MB2737 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Rob=0A= =0A= > > On Fri, Aug 20, 2021 at 06:39:06PM +0900, Shunsuke Nakamura wrote:=0A= > > > perf_evsel__read() scales counters obtained by RDPMC during multiplex= ing, but=0A= > > > does not scale counters obtained by read() system call.=0A= > > > =0A= > > > Add processing to perf_evsel__read() to scale the counters obtained d= uring the=0A= > > > read() system call when multiplexing.=0A= > > =0A= > > Which one is right though? Changing what read() returns could break =0A= > > users, right? Or are you implying that the RDPMC path is correct and = =0A= > > read() was not. More likely the former case since I wrote the latter.= =0A= > =0A= > perf_evsel__read() returns both the count obtained by RDPMC and the count= obtained=0A= > by the read() system call when multiplexed with RDPMC enabled.=0A= > =0A= > That is, there is a mix of scaled and unscaled values.=0A= > =0A= > As Rob says, when this patch is applied, rescaling the count obtained fro= m=0A= > perf_evsel__read() during multiplexing will break the count.=0A= > =0A= > I think the easiest solution is to change the value you get from RDPMC to= not scale =0A= > and let the user scale it, but I thought it would be a little inconvenien= t.=0A= =0A= Any comments?=0A= =0A= Best Regards=0A= Shunsuke=