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Tue, 24 Mar 2020 22:25:37 +0000 From: Song Liu To: linux-kernel CC: Kernel Team , Peter Zijlstra , Arnaldo Carvalho de Melo , Jiri Olsa , Alexey Budankov , Namhyung Kim , Tejun Heo Subject: Re: [PATCH v11] perf: Sharing PMU counters across compatible events Thread-Topic: [PATCH v11] perf: Sharing PMU counters across compatible events Thread-Index: AQHWAiT9KEupE+dDF0SaZgMOIv1+LqhYRjSAgAALyQA= Date: Tue, 24 Mar 2020 22:25:37 +0000 Message-ID: <92D9FFD5-D381-4E46-92BE-F981F0F91388@fb.com> References: <20200324214125.153584-1-songliubraving@fb.com> <4359BCB5-1FB5-4A5A-B528-10CDDA97A5DF@fb.com> In-Reply-To: <4359BCB5-1FB5-4A5A-B528-10CDDA97A5DF@fb.com> 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) x-originating-ip: [2620:10d:c090:400::5:393e] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: ac079969-b72a-4660-fb94-08d7d0424741 x-ms-traffictypediagnostic: MW3PR15MB3963: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-fb-source: Internal x-ms-oob-tlc-oobclassifiers: OLM:3173; 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charset="us-ascii" Content-ID: <7B633632D4FF5F46A7AEF8E3AE984A07@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: ac079969-b72a-4660-fb94-08d7d0424741 X-MS-Exchange-CrossTenant-originalarrivaltime: 24 Mar 2020 22:25:37.5860 (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: xS4AS0Ik26VnRmp0yFuREFFKMhlI1xzZpqehjQksRdq1bcfMYl1RJcMf6Oi+pcLTFg6y0WARV2T6z8V39b5s8g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR15MB3963 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.645 definitions=2020-03-24_09:2020-03-23,2020-03-24 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 bulkscore=0 lowpriorityscore=0 mlxlogscore=999 spamscore=0 phishscore=0 suspectscore=0 clxscore=1015 adultscore=0 mlxscore=0 impostorscore=0 malwarescore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003240111 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Mar 24, 2020, at 2:43 PM, Song Liu wrote: >=20 >=20 >=20 >> On Mar 24, 2020, at 2:41 PM, Song Liu wrote: >>=20 >> This patch tries to enable PMU sharing. When multiple perf_events are >> counting the same metric, they can share the hardware PMU counter. We >> call these events as "compatible events". >>=20 >> The PMU sharing are limited to events within the same perf_event_context >> (ctx). When a event is installed or enabled, search the ctx for compatib= le >> events. This is implemented in perf_event_setup_dup(). One of these >> compatible events are picked as the master (stored in event->dup_master)= . >> Similarly, when the event is removed or disabled, perf_event_remove_dup(= ) >> is used to clean up sharing. >>=20 >> If the master event is a cgroup event or a event in a group, it is >> possible that some slave events are ACTIVE, but the master event is not. >> To handle this scenario, we introduced PERF_EVENT_STATE_ENABLED. Also, >> since PMU drivers write into event->count, master event needs another >> variable (master_count) for the reading of this event. >>=20 >> On the critical paths (add, del read), sharing PMU counters doesn't >> increase the complexity. Helper functions event_pmu_[add|del|read]() are >> introduced to cover these cases. All these functions have O(1) time >> complexity. >>=20 >> Cc: Peter Zijlstra >> Cc: Arnaldo Carvalho de Melo >> Cc: Jiri Olsa >> Cc: Alexey Budankov >> Cc: Namhyung Kim >> Cc: Tejun Heo >> Reported-by: kernel test robot >> Signed-off-by: Song Liu >>=20 >> --- >> Changes in v12: >> Fix new failures perf_event_tests. (kernel test robot) >=20 > Typo in subject. This is actually v12.=20 I was stupid... This version didn't work... Please discard it.=20 Song