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Wed, 29 Sep 2021 16:35:35 +0000 From: "Liang, Kan" To: Peter Zijlstra , Song Liu CC: Like Xu , bpf , Networking , Kernel Team , Andrii Nakryiko , Alexei Starovoitov , "like.xu@linux.intel.com" , Andi Kleen Subject: RE: bpf_get_branch_snapshot on qemu-kvm Thread-Topic: bpf_get_branch_snapshot on qemu-kvm Thread-Index: AQHXtUsCll+d9db2OEyfPrzZnzZB7Ku7M+DQ Date: Wed, 29 Sep 2021 16:35:35 +0000 Message-ID: References: <0E5E6FCA-23ED-4CAA-ADEA-967430C62F6F@fb.com> In-Reply-To: Accept-Language: en-CA, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-version: 11.5.1.3 dlp-product: dlpe-windows dlp-reaction: no-action authentication-results: infradead.org; dkim=none (message not signed) header.d=none;infradead.org; dmarc=none action=none header.from=intel.com; x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: dcf0fec3-64a3-491f-2230-08d9836729eb x-ms-traffictypediagnostic: SJ0PR11MB4928: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:9508; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SJ0PR11MB4814.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: dcf0fec3-64a3-491f-2230-08d9836729eb X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Sep 2021 16:35:35.6945 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: Hl268Grd2irNFa/Uu5A3yN1hh1Fcw81HQhU2jTvnmLYFW3BlDA3R11MVoUT7iXbjwoktpj4ZeMfSaCy+NMGhqA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR11MB4928 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org > > > - get confirmation that clearing GLOBAL_CTRL is suffient to supress > > > PEBS, in which case we can simply remove the PEBS_ENABLE clear. > > > > How should we confirm this? Can we run some tests for this? Or do we > > need hardware experts' input for this? >=20 > I'll put it on the list to ask the hardware people when I talk to them ne= xt. But > maybe Kan or Andi know without asking. If the GLOBAL_CTRL is explicitly disabled, the counters do not count anymor= e. It doesn't matter if PEBS is enabled or not.=20 See 6c1c07b33eb0 ("perf/x86/intel: Avoid unnecessary PEBS_ENABLE MSR access in PMI "). We optimized the PMU handler base on it. Thanks, Kan