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;
Message-ID: <c093d8b2-d6c6-237c-ffd4-0cb1565e971c@intel.com>
Date:   Thu, 11 May 2023 14:37:37 -0700
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Firefox/102.0 Thunderbird/102.10.1
Subject: Re: [PATCH v1 4/9] x86/resctrl: Flush MBM event counts on soft RMID
 change
Content-Language: en-US
To:     Peter Newman <peternewman@google.com>,
        Fenghua Yu <fenghua.yu@intel.com>
CC:     Babu Moger <babu.moger@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Stephane Eranian <eranian@google.com>,
        James Morse <james.morse@arm.com>,
        <linux-kernel@vger.kernel.org>, <linux-kselftest@vger.kernel.org>
References: <20230421141723.2405942-1-peternewman@google.com>
 <20230421141723.2405942-5-peternewman@google.com>
From:   Reinette Chatre <reinette.chatre@intel.com>
In-Reply-To: <20230421141723.2405942-5-peternewman@google.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?VElFVDdsaW4wZFdpc3NYYXJaNkwxdmhPZXZieEh4cDgybGVWRXFRaXZPSWRX?=
 =?utf-8?B?QVFxVXVyWHVvbXlaTW5QeXVhNU55OGhjVllGL2FhdlFOUVRhNzAxYThjaVYv?=
 =?utf-8?B?ZGVjUWFnZVdtS3F2Wk56ZnM5NE10Sm4yekhjUHd5WWZnTWphVFJiMS82WjMx?=
 =?utf-8?B?aHZGOXF3T2dKbTlTV3V3R2Z4a0kvQ3RDaStvRGpjZWpNWm9QTnkwWS80WmdM?=
 =?utf-8?B?ZVNTemNMMmpTb0w4ODY0emVlTjNwZUU3b200VGxCOE9pNnUwMFcyRlVhUjEv?=
 =?utf-8?B?aXRCeFdtd3FQRjg5RUNaUTQxV3ZOVHJuWlVqRVNYbmtYUkxvOHIyUERVZ0xa?=
 =?utf-8?B?bkV5K0E5Sld0WmxJaW01VXpCK1FseHZaRWUrb2tpZUxOOUtCSjBScVhtbjli?=
 =?utf-8?B?L3R6TjgvVmR5U3l6bDM2Rjh0OHVqZmV2T0diT2lwdzJ0WGRhM2F0dWo5Q2Jr?=
 =?utf-8?B?MmQxSzh3Q2hEaS9LZnV3MDV2NUszbnV0S3IzY3VkVUVEcnlZT0pPQ2o2Tkl2?=
 =?utf-8?B?bFJGVHlueExpUy9NdTJURlVQcEJSeTRMM2YwK0lpbng5NGswV0NzaEFRMGpw?=
 =?utf-8?B?NXk0ZGFrWUhaVURzcDcvb2FyRzI5ZXd3MFFyT2QvbUhpZDBBcEMvVzA3MmVQ?=
 =?utf-8?B?b01oNjFQbnNyOWJOYWVjcUF6bVNWOXBoZDIxaHJ4a1lNc2ZzSi80eDNYZlFu?=
 =?utf-8?B?a2IwMmtqd2JQd2hjWUtnR3JnTnROc3liMWVCT1JaZUJDWkVVZjRIa2FNU1JV?=
 =?utf-8?B?aVpRR09saFZEU1ltRHo1d0dwM1VJbERyS1hSQ2xWcEorTEwyMDc0NjBNdGJR?=
 =?utf-8?B?bzAvQXNjQXkwVVVTeTJQV1FEZ0VGNFdLaVdROVd0K3J1WVZ6aG9URjkwY1dR?=
 =?utf-8?B?L2Z3TW9NSTRUMk5lUUZIMWJkYU9GdCtpSWJmMGttZG9ZQVdBTVdEQS9HTWo1?=
 =?utf-8?B?RUZZNHAydS9ESlp4T2hINWdaTi8wN2V3Y095bUpIWUNLZFl0aTNNeUlUVzI3?=
 =?utf-8?B?eDhVWWtVUE1QcmQ3eWx2RENJV0d6M21GRHR4QVVzZWQ1M09hb0RPK05PcFZT?=
 =?utf-8?B?Z050NHBVSGhScU9GOGEvUmtoMFZLVTZHL0lYVFRLRk1KUVZNdE5iOTNJVkI5?=
 =?utf-8?B?VVN2UEh3U0hVRGZXd1cwTDFKVlRYMVdOZnlVbTEvQURNZ0tsMXBJLy9kampn?=
 =?utf-8?B?b25RM1JVdkJxbUdVeVlONXRRQlFTMGU1MDQ1Y2dKRnVqUXBYRmV3TUllNWQ3?=
 =?utf-8?B?UlNtdVJBcEtKNjRoUzVzdkZwWExrbGRHV2NvTjJmOXMwTDdWVlVDMWpBUG5H?=
 =?utf-8?B?Tm01N0ppSXhYUVdnRTd3OVFyZllKTVNPVzBRdlVtYWRtYkRoUmxlYm5vMWxF?=
 =?utf-8?B?QmlydDlKMURJT3FJbm5DZE9QZVg2TlFOOC9Wc0o4cWY4dGxPSk1YWjdNN1M5?=
 =?utf-8?B?OEFsWHFyWk5pT1lqUE1TR2RmcUJwYTFQMFEreHV5ai9EY3hodEZvZ2FJV2RP?=
 =?utf-8?B?cVV3bCtMdGRGMk9wUVYzWW03dExaRzJEekJzZGRqeXRUcHhWSG9wTm9OeSs1?=
 =?utf-8?B?azdteGo4TkVDTHA3N2JnTUM4UFBMdEFhbWFpanZLVnNFRjhUdU9GQW4vWitY?=
 =?utf-8?B?dERDZ2FuZTRIVnNHTXFvbjhtWCtpd1ZQLzVCNXNhdUN5V0E0eXdlWTVaeHlN?=
 =?utf-8?B?ekVVRjVDYUVxUks3Nkd6VzVlUjVZWWI0Z0hVVXpQYk9Pdlh0UFhRNldsbzI5?=
 =?utf-8?B?NmtBajVIRzRnVUlxYTJFWHFseEs5N0YwRFBVZzNSbEt0eVhRc3NQUVJvWXZl?=
 =?utf-8?B?LzFDdENQZ3oyOTF4dGFvNDVCd1phYlhUWXJHNmZsOS9WYUlTMVRMQnIwMHZr?=
 =?utf-8?B?QUMzRk54R0I1TkoyZVlIaFNJYnppOG9GcFVKaW9MOUx2UFBSazZYZ1NjSDNE?=
 =?utf-8?B?UVNZVGN5bmEwQlF0d2VpUUdXd1JOaHpyNHZFYitXUHZISm1GZytzNnRTK2Nw?=
 =?utf-8?B?bU9KTHI5dklDdU05MHNIRGhwaXpWbXVidjRmUkl4Q2VpV2Q2S21kdUs1NDlZ?=
 =?utf-8?B?UFJhQW1VNG5SSDMzeUJpWlp5cnNzellnL3BXdDg5cE1TUVFta0NTcHc2NVVt?=
 =?utf-8?B?ei83YTI0WXBRMXk3UXBvQU5ZT29zQm5COUxDVU5DUEd1L0tQVUJqS1Y5T05v?=
 =?utf-8?B?M1E9PQ==?=
X-MS-Exchange-CrossTenant-Network-Message-Id: bf8bce98-dbb4-47a2-e707-08db5267f159
X-MS-Exchange-CrossTenant-AuthSource: SJ2PR11MB7573.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 May 2023 21:37:38.8894
 (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: Jw9LT3mpD3M51AgUxBx2IEx0RggFalDG6qCuqObEQaeFz8J0BTla4i+4OKgrxxdYZodKTu8xNSUtSC/68es+txA8z1UF+F7mSMgRHZSXWWY=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN0PR11MB5964
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-6.5 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,
        RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,
        SPF_NONE,T_SCC_BODY_TEXT_LINE 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

Hi Peter,

On 4/21/2023 7:17 AM, Peter Newman wrote:
> To implement soft RMIDs, context switch must detect when the current
> soft RMID is changing and if so, flush the CPU's MBM event counts to the
> outgoing soft RMID.
> 
> To avoid impacting context switch performance in the non-soft RMID case,
> protect the new logic with a static branch.
> 
> Co-developed-by: Stephane Eranian <eranian@google.com>
> Signed-off-by: Stephane Eranian <eranian@google.com>
> Signed-off-by: Peter Newman <peternewman@google.com>
> ---
>  arch/x86/include/asm/resctrl.h         | 27 +++++++++++++++++++++++++-
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c |  1 +
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
> index e7acf118d770..50d05e883dbb 100644
> --- a/arch/x86/include/asm/resctrl.h
> +++ b/arch/x86/include/asm/resctrl.h
> @@ -36,6 +36,9 @@ DECLARE_PER_CPU(struct resctrl_pqr_state, pqr_state);
>  DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
>  DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
>  DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
> +DECLARE_STATIC_KEY_FALSE(rdt_soft_rmid_enable_key);
> +
> +void resctrl_mbm_flush_cpu(void);
>  
>  /*
>   * __resctrl_sched_in() - Writes the task's CLOSid/RMID to IA32_PQR_MSR
> @@ -75,9 +78,31 @@ static inline void __resctrl_sched_in(struct task_struct *tsk)
>  	}
>  
>  	if (closid != state->cur_closid || rmid != state->cur_rmid) {
> +		if (static_branch_likely(&rdt_soft_rmid_enable_key)) {

Could you please elaborate on the choice of static_branch_likely() (as opposed
to static_branch_unlikely())?

Reinette