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Wed, 29 Apr 2020 20:44:54 +0000 From: Song Liu To: Peter Zijlstra CC: linux-kernel , Kernel Team , Arnaldo Carvalho de Melo , Jiri Olsa , Alexey Budankov , Namhyung Kim , Tejun Heo , "kernel test robot" Subject: Re: [PATCH v12] perf: Sharing PMU counters across compatible events Thread-Topic: [PATCH v12] perf: Sharing PMU counters across compatible events Thread-Index: AQHWBzHW5dF+e/R99EaK1PXwCxhLFqiCwbOAgA39+wA= Date: Wed, 29 Apr 2020 20:44:54 +0000 Message-ID: References: <20200331075533.2347393-1-songliubraving@fb.com> <20200420230429.GT2483@worktop.programming.kicks-ass.net> In-Reply-To: <20200420230429.GT2483@worktop.programming.kicks-ass.net> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3608.60.0.2.5) authentication-results: infradead.org; dkim=none (message not signed) header.d=none;infradead.org; dmarc=none action=none header.from=fb.com; x-originating-ip: [2620:10d:c090:400::5:a135] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 453268ad-13f9-4ea2-e3ee-08d7ec7e2c1f x-ms-traffictypediagnostic: BYAPR15MB2999: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-fb-source: Internal x-ms-oob-tlc-oobclassifiers: OLM:4714; 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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 453268ad-13f9-4ea2-e3ee-08d7ec7e2c1f X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Apr 2020 20:44:54.5127 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: TCeRd2L36qk+pI/+KvqKIOvRH3c7D4fFouwD+9s0Spv5miRhfPT57q0l1rZW1QhKSPMsKV3abGVvAZ3QcYRQAQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2999 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.676 definitions=2020-04-29_10:2020-04-29,2020-04-29 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 clxscore=1011 impostorscore=0 lowpriorityscore=0 suspectscore=0 priorityscore=1501 mlxlogscore=999 malwarescore=0 phishscore=0 mlxscore=0 adultscore=0 spamscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004290149 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Apr 20, 2020, at 4:04 PM, Peter Zijlstra wrote: >>=20 >> static inline u64 perf_event_count(struct perf_event *event) >> { >> - return local64_read(&event->count) + atomic64_read(&event->child_count= ); >> + u64 count; >> + >> + if (likely(event->dup_master !=3D event)) >> + count =3D local64_read(&event->count); >> + else >> + count =3D local64_read(&event->master_count); >> + >> + return count + atomic64_read(&event->child_count); >> } >=20 > So lsat time I said something about SMP ordering here. Where did that > go? I am not quite sure about this one. I guess the following is sufficient.=20 Could you please help me double check?=20 Thanks, Song static inline u64 perf_event_count(struct perf_event *event) { struct perf_event *master; u64 count; again: master =3D READ_ONCE(event->dup_master); if (master =3D=3D EVENT_TOMBSTONE) goto again; if (likely(master !=3D event)) count =3D local64_read(&event->count); else count =3D local64_read(&event->master_count); return count + atomic64_read(&event->child_count); }