Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Song Liu <songliubraving@meta.com>
To:     Peter Zijlstra <peterz@infradead.org>
CC:     Song Liu <song@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Kernel Team <kernel-team@meta.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2] watchdog: Prefer use "ref-cycles" for NMI watchdog
Thread-Topic: [PATCH v2] watchdog: Prefer use "ref-cycles" for NMI watchdog
Thread-Index: AQHZiFJQA17dibxJREeMwvRcxvYa+a9eEn+AgACtGAA=
Date:   Wed, 17 May 2023 17:51:01 +0000
Message-ID: <1DEE93B2-BA74-4266-A3C1-22A9DDEB63A8@fb.com>
References: <20230516235817.2323062-1-song@kernel.org>
 <20230517073119.GA2665450@hirez.programming.kicks-ass.net>
In-Reply-To: <20230517073119.GA2665450@hirez.programming.kicks-ass.net>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?YN71BiywDUj/oKHw0XdriBlK40BQN1Cb9wALJrU/aPcrQyCSewQZiBp7nWgo?=
 =?us-ascii?Q?G2cn1TeXvO0lpdTN7pD3xogBmq9oaapByJxHcpSljZIyiMwa4hWwXDhgc5eh?=
 =?us-ascii?Q?bk26QduXTckEkzHO9UfxaqbDuPabRVMrH4oLPY6uOu8GPlsuXWQwwQGJzwvy?=
 =?us-ascii?Q?w9wEvgkRODCUw0e6wvXCQsbG9+zv5Nvgcx4SSNaF6pdKX6v6G8mEfvx34lKu?=
 =?us-ascii?Q?hj98W9pa5LuVwnFeovCvVUV+rnkTpxOHZa6bQJojwZg3bL+l4lcATuh0Vi9w?=
 =?us-ascii?Q?D573rVsux7FDrSk1wBUnL0gAgxtdi840Eh/U9Eul/C64JC4IadCtAsUGYzrr?=
 =?us-ascii?Q?X4mi7QKaMLb5Fr3H/2WLh/Gi/Ppcgp1/3Vgn5vrjdUa/edXC3rNn7p0jShrD?=
 =?us-ascii?Q?yaJngrKfNgwhvp/wTile//tGTyoSeUk9efd0L5whkxYVaK4c5x4VLsMqgXpc?=
 =?us-ascii?Q?NRAIqfIYQAga7arRml+OjBvgKyVzOUs6IBJNGfDIG57Yso/FgPsu+QWYo1pj?=
 =?us-ascii?Q?6rrsKfx96+B5mB01IObd7cEk1Lxe/37yoZSXKmNYIWsMBPne4RG/LkHmwF0a?=
 =?us-ascii?Q?g/HqDQQOp85Tg61R5w4RC5XtCo+8mjvf3t7S7lc39QMhekWgOugIpwl04yFo?=
 =?us-ascii?Q?64owWVuT3ncwxhaqCEEbwcUP+yQA+ZT3zoefrl8gmYcanDdq93QeXNjrZust?=
 =?us-ascii?Q?w2IufkvkVHCNd5anWBh9kDYmNcxjsDhkWZ/j7G0SMpDP56D2hZifcrLOlCwz?=
 =?us-ascii?Q?GI3UVwLmKcDoTV8owUCefDGJLkvr03zK2beAztz4v6FExSAXCYGSqK7kpA8y?=
 =?us-ascii?Q?zeagpNeBptnz12PqVvRjuQP+DvhtQNbqWm0/5QOIzYtJvNI3rtwjBRxPspBl?=
 =?us-ascii?Q?MD46+8bmCGfz9h6MT3PGHeZT9Wgo/XF5FaL/pZS+besq7rIYt1csgaoL4tmr?=
 =?us-ascii?Q?ySLg56EI/+dsNwyxMSPA9TOP8LUJFDUejxWqresc93JbBBGxeHJpIrBoXdy9?=
 =?us-ascii?Q?BR0FHT6qGrvQzJ1j/fh7CwmJ0CSpggAdXOvxQtI3OnyQ8dAsAtqRDkBDaqCn?=
 =?us-ascii?Q?+YhviAQv4IDo34xFAaYdd14JMoeWDVlNiuaMPFcH9UUV1o7Me7ysYx8yK8gu?=
 =?us-ascii?Q?9JxZU3uQ+kXa5ShW5jdSLHhoZGHMNsdB/+agEN5MGV0NioK8N/R+vahn+y7T?=
 =?us-ascii?Q?B5cwdDpPCz3FmLimutfbWLG6l5zUkbG2fUzkEPVZNq44WEFC4a6Jp775FT0+?=
 =?us-ascii?Q?ctCoxtKZT3xzTBSTzKYYfFN+piJjY+JpzWTWVLMBFJ3we0/H7IOtq9hiL8fm?=
 =?us-ascii?Q?ildUMxMyU0x5fLZfav987dPQOtSId43+IMHs+aNSBXBsxWfbQfHCM0cDwT8V?=
 =?us-ascii?Q?wnnVniyxgDYyEibthqaaHeUKtkQXL05ITSbsecoCL64vgLI+pVpPHzNMrmLT?=
 =?us-ascii?Q?Jh3qA0BRwbUWnxq8q7tKKtwgdLd2Ww54LoL+s4ZTnDiJyswpwY4BKvtNuqpi?=
 =?us-ascii?Q?r8wEHtk9LNFwkC/aRJ+QDO5Wph7jejfqT1XR2ospPHhfcPzTY1Rja+zmiQHD?=
 =?us-ascii?Q?283lLoaqO8XHanZ4QkqOo9QG5h2atnhkJksht31JjV3MYZHuIuLOw3nUO7c+?=
 =?us-ascii?Q?CKshGHflOBbQY6OvLOFIz5Q=3D?=
Content-Type: text/plain; charset="us-ascii"
Content-ID: <6A08F874D5F7C74DAB82FD049F58C7E1@namprd15.prod.outlook.com>
MIME-Version: 1.0
X-OriginatorOrg: meta.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: SA1PR15MB5109.namprd15.prod.outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 73a2a6d9-f50b-43aa-784f-08db56ff470b
X-MS-Exchange-CrossTenant-originalarrivaltime: 17 May 2023 17:51:01.1372
 (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: XZ7nCC0mdDEN913MSe4n12eJvlnj5GAz/Wh0uARTtsNA9KSUmtnGEA99lM2Ss4OWQs80utVnElC9bhjwb0ifsw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR15MB6162
X-Proofpoint-GUID: N9jdcN2RXLvk7i5s4HF13j5xEZxe6WkK
X-Proofpoint-ORIG-GUID: N9jdcN2RXLvk7i5s4HF13j5xEZxe6WkK
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.170.22
 definitions=2023-05-17_02,2023-05-17_02,2023-02-09_01
X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,
        RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_PASS,
        T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no
        version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


> On May 17, 2023, at 12:31 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> On Tue, May 16, 2023 at 04:58:17PM -0700, Song Liu wrote:
>> NMI watchdog permanently consumes one hardware counters per CPU on the
>> system. For systems that use many hardware counters, this causes more
>> aggressive time multiplexing of perf events.
>> 
>> OTOH, some CPUs (mostly Intel) support "ref-cycles" event, which is rarely
>> used. Try use "ref-cycles" for the watchdog, so that one more hardware
>> counter is available to the user. If the CPU doesn't support "ref-cycles",
>> fall back to "cycles".
>> 
>> The downside of this change is that users of "ref-cycles" need to disable
>> nmi_watchdog.
> 
> I still utterly hate how you hardcode ref-cycles

OK.. let me try with kernel cmdline args. Sending v3. 

Thanks,
Song