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;
Date:   Wed, 11 Jan 2023 15:21:38 -0800
From:   Ashok Raj <ashok.raj@intel.com>
To:     "Luck, Tony" <tony.luck@intel.com>
CC:     "Moger, Babu" <Babu.Moger@amd.com>,
        Ashok Raj <ashok_raj@linux.intel.com>,
        "corbet@lwn.net" <corbet@lwn.net>,
        "Chatre, Reinette" <reinette.chatre@intel.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "bp@alien8.de" <bp@alien8.de>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        "dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
        "x86@kernel.org" <x86@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>,
        "paulmck@kernel.org" <paulmck@kernel.org>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "quic_neeraju@quicinc.com" <quic_neeraju@quicinc.com>,
        "rdunlap@infradead.org" <rdunlap@infradead.org>,
        "damien.lemoal@opensource.wdc.com" <damien.lemoal@opensource.wdc.com>,
        "songmuchun@bytedance.com" <songmuchun@bytedance.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "jpoimboe@kernel.org" <jpoimboe@kernel.org>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "Bae, Chang Seok" <chang.seok.bae@intel.com>,
        "pawan.kumar.gupta@linux.intel.com" 
        <pawan.kumar.gupta@linux.intel.com>,
        "jmattson@google.com" <jmattson@google.com>,
        "daniel.sneddon@linux.intel.com" <daniel.sneddon@linux.intel.com>,
        "Das1, Sandipan" <Sandipan.Das@amd.com>,
        "james.morse@arm.com" <james.morse@arm.com>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "bagasdotme@gmail.com" <bagasdotme@gmail.com>,
        "Eranian, Stephane" <eranian@google.com>,
        "christophe.leroy@csgroup.eu" <christophe.leroy@csgroup.eu>,
        "jarkko@kernel.org" <jarkko@kernel.org>,
        "Hunter, Adrian" <adrian.hunter@intel.com>,
        "quic_jiles@quicinc.com" <quic_jiles@quicinc.com>,
        "peternewman@google.com" <peternewman@google.com>,
        Ashok Raj <ashok.raj@intel.com>
Subject: Re: [PATCH v11 01/13] x86/resctrl: Replace smp_call_function_many()
 with on_each_cpu_mask()
Message-ID: <Y79Egt98ZoWTr3Nl@a4bf019067fa.jf.intel.com>
References: <20230109164405.569714-1-babu.moger@amd.com>
 <20230109164405.569714-2-babu.moger@amd.com>
 <Y7yiwOerGiEKAF9i@araj-dh-work>
 <MW3PR12MB4553FFAA412FB741A73009A195FF9@MW3PR12MB4553.namprd12.prod.outlook.com>
 <DS7PR11MB60772F09B9749307CFA0ED0DFCFF9@DS7PR11MB6077.namprd11.prod.outlook.com>
 <Y77ZAfhc48W41FGp@a4bf019067fa.jf.intel.com>
 <SJ1PR11MB6083AA5292C11145BEEBAF6FFCFC9@SJ1PR11MB6083.namprd11.prod.outlook.com>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <SJ1PR11MB6083AA5292C11145BEEBAF6FFCFC9@SJ1PR11MB6083.namprd11.prod.outlook.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?UjkS2VQ1jdwwDQGShu0I8FKiRHzb3+ITKInB2pm15H8lb5xuugqT/TLCtCBG?=
 =?us-ascii?Q?n3n9XA8nVsC2iqGKw1Rf8goEpiNT6JntwytBxuvJ6qDO8c3JxBA+kllBxzJx?=
 =?us-ascii?Q?d+isR/FhKLanLXbNqfflcuNbhM7Es4GGmK0rGLBTtg0o44G5guQ3nBkJowMQ?=
 =?us-ascii?Q?Ox9F2ujoPUvc0s9MOmPBiw1AsChpfUeu27xZJ3YgyLTZfqfXa2nAuDtmTtiZ?=
 =?us-ascii?Q?c54auPXemM2g4FHACqgPQvB9APbgZFvERpsu7VbF5rc/HeEMOFfX1TzHst1L?=
 =?us-ascii?Q?CoSqBZkdnqdexjM1sNOc7kDreXHk7uYtAPNSBJxKFpbZpSkMyMuxuD1JT3s7?=
 =?us-ascii?Q?v3C/pT5D77BxhtjkNy96KN687DgfXhN0fOqPaFt8OkJI0Cj3VTojCVfFBPxd?=
 =?us-ascii?Q?S4G3c6p541UUROrolZUcd5NLmUrvgEK1b+sR3gWPoVPzOr+MmtxhuWE/lq7q?=
 =?us-ascii?Q?cBYpBB4a9NDd80vlUzuV86rW1OK5/XackrNd9gji+9M7xEpAPEnjgNe9bMr7?=
 =?us-ascii?Q?KpHAzKS9wAtfKfJFOrL/Gf+87Bqheufb4KelMO7n7NqImkAqB1zzA8m9dls5?=
 =?us-ascii?Q?N/TRCpz2sJHs9CmdQ6OutKN0p/FZ5DV90r9kxpdI0za1U9mRTCx4XKs5P6Pd?=
 =?us-ascii?Q?yI7Gri4td4mDyUp7gkNwiTxcXNDPwq7z1OUMHYL8sz1YkNi+x7Hv3o8pVgo+?=
 =?us-ascii?Q?T8fv8WMUBijdOuLcJ7sJ0k/OB0Na3+/aizMEmTtkcRfKuk2TUf4wiV3KeRBB?=
 =?us-ascii?Q?g/EZQPTHNrxh9Tl81j+unSsWsNUao2zQlKQDcGbdW1jti0K0QhuY7u+bzroG?=
 =?us-ascii?Q?JMMAGUgLFEUcz9nIu5SZ/oU1bUteTlwzCZfzaH5ZqQVmV+DV0gGqqWxDIhou?=
 =?us-ascii?Q?toiJnSvoSLSqmry9Kpuz1p7qPgB/OnfCxf+zrCSgAqdjgQfsKaW2Dlzb0YQz?=
 =?us-ascii?Q?WdW6zwMIAhhMfGNtedOe6VyI8THXHZ7pgEIyXpwIO8ApsgvO9E+at15uc2AJ?=
 =?us-ascii?Q?iLffxvPx/vypoWCr8JeJJ0xE6VPC/RpWFXPlS+zr/Zmkp/ar7a68IJTSk9iH?=
 =?us-ascii?Q?0AHax/yFDbOPZO5pUpk4mAEiRujfnpCW42VUnn9NMnBpOp85AofAxGeKao6J?=
 =?us-ascii?Q?tRCbHMUfCLpPoBmYtvwHER2vg6dQ5OjgDvn3ThMaz0ssaFuybSKLb7vowP9L?=
 =?us-ascii?Q?TbDWreh+CjWIK3H1RvtYj/TwKuKxwJeoqSxfq8Zo9kfsOfi6mgKsCdMh4HbX?=
 =?us-ascii?Q?pROOngQCozv1zz16BQftjQq3lffeUGTctaKXIB+1UiGkXWeQfoBrT7Ebw2D1?=
 =?us-ascii?Q?r35hEw1AZBG6XJQkt1uuIIzzKFAGPnzAAE8Flr0EYRCLkBSgSqZQj0P1RzYh?=
 =?us-ascii?Q?Mhy/c17kWPdP1IYcOm6ydIgkj8n3QEh8TaEc2rHikwDzT5l1O8/SFGKg1/l6?=
 =?us-ascii?Q?2aNa8FxVyFcdw9cL62A5Cu2AryPXCYBSPY23GPmrud0WR0wq49VE8DoaxXFT?=
 =?us-ascii?Q?DFtW1E2cfEFDxCrx1zYKpIHEdVEixJhNMAK/BHTIN5DiJqpUE50kUndytjhv?=
 =?us-ascii?Q?nrC6sZ/jH5VXRoCfh3/IEHJC/erlxnAG8De13MnjP2DgzF8xh5OChyzs1kOa?=
 =?us-ascii?Q?VQ=3D=3D?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 59b5e784-7816-4f97-abaa-08daf42a9910
X-MS-Exchange-CrossTenant-AuthSource: SJ1PR11MB6201.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Jan 2023 23:21:42.1543
 (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: BFCSvaX1hHkiaXPh6hsPviTbaUJPjnT75Rghq0nuaqpXuvPnQXcMSVx9yXbrKv2GPSu9z8UFP2ogDtsSJqZI0g==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN9PR11MB5259
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,
        RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE
        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 Wed, Jan 11, 2023 at 11:05:48AM -0800, Tony Luck wrote:
> > I wasn't sure if the few ms difference is going to make much material
> > difference for that process. IPI's does shake things up and introduces
> > other overheads not related to this process.
> 
> Is it just a few milli-seconds? What is the scheduler priority of the kernel
> thread you wake to perform this action? How does that compare to the
> priority of a RT thread?  I may be wrong here, but I think an RT thread can
> block a kernel thread from running indefinitely.

That's a good point. I don't have an idea about how the kernel thread
priority is compared to user space RT threads.

I assumed that since these threads have some work to be done from kernel,
user space shouldn't get higher priority than kernel tasks.

Uncharted territory for me ... Just a hunch :)

Maybe @peterz can screw my head in the right direction :-)