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Thu, 6 Feb 2025 18:05:35 +0000 Message-ID: Date: Thu, 6 Feb 2025 10:05:32 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 19/23] x86/resctrl: Introduce the interface to switch between monitor modes To: Babu Moger , , , , , , , CC: , , , , , , , , , , , , , , , , , , , , , , , , References: From: Reinette Chatre Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR03CA0243.namprd03.prod.outlook.com (2603:10b6:303:b4::8) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ2PR11MB7573:EE_|CH3PR11MB8702:EE_ X-MS-Office365-Filtering-Correlation-Id: 8a859b70-6fd4-4aca-4857-08dd46d8dac4 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|366016|376014|7053199007; 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In mbm_cntr_assign, monitoring event can only accumulate data > while it is backed by a hardware counter. In 'default' mode, resctrl > assumes there is a hardware counter for each event within every CTRL_MON > and MON group. > > Introduce interface to switch between mbm_cntr_assign and default modes. > > $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode > [mbm_cntr_assign] > default > > To enable the "mbm_cntr_assign" mode: > $ echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode > > To enable the default monitoring mode: > $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode > > MBM event counters are automatically reset as part of changing the mode. > Clear both architectural and non-architectural event states to prevent > overflow conditions during the next event read. > > Signed-off-by: Babu Moger > --- > --- > Documentation/arch/x86/resctrl.rst | 25 ++++++++++++- > arch/x86/kernel/cpu/resctrl/rdtgroup.c | 50 +++++++++++++++++++++++++- > 2 files changed, 73 insertions(+), 2 deletions(-) > > diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst > index 072b15550ff7..5d18c4c8bc48 100644 > --- a/Documentation/arch/x86/resctrl.rst > +++ b/Documentation/arch/x86/resctrl.rst > @@ -259,7 +259,10 @@ with the following files: > > "mbm_assign_mode": > Reports the list of monitoring modes supported. The enclosed brackets > - indicate which mode is enabled. > + indicate which mode is enabled. The MBM events (mbm_total_bytes and/or > + mbm_local_bytes) associated with counters may reset when "mbm_assign_mode" > + is changed. > + > :: > > # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode > @@ -275,6 +278,16 @@ with the following files: > available is described in the "num_mbm_cntrs" file. Changing the mode > may cause all counters on a resource to reset. > > + Moving to mbm_cntr_assign mode require users to assign the counters to > + the events. Otherwise, the MBM event counters will return "Unassigned" > + when read. Again ... please be consistent in using single or double quotes for information returned from file. > + > + The mode is beneficial for AMD platforms that support more CTRL_MON > + and MON groups than available hardware counters. By default, this > + feature is enabled on AMD platforms with the ABMC (Assignable Bandwidth > + Monitoring Counters) capability, ensuring counters remain assigned even > + when the corresponding RMID is not actively used by any processor. > + > "default": > > In default mode, resctrl assumes there is a hardware counter for each > @@ -283,6 +296,16 @@ with the following files: > "mbm_total_bytes" or "mbm_local_bytes" will report 'Unavailable' if > there is no counter associated with that event. > > + * To enable "mbm_cntr_assign" mode: > + :: > + > + # echo "mbm_cntr_assign" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode > + > + * To enable default monitoring mode: > + :: > + > + # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode > + Please be consistent in the documentation. To enable "mbm_cntr_assign" mode: To enable "default" mode: or To enable "mbm_cntr_assign" monitoring mode: To enable "default" monitoring mode: or ...? > "num_mbm_cntrs": > The number of monitoring counters available for assignment when the > system supports mbm_cntr_assign mode. > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > index f61f0cd032ef..6922173c4f8f 100644 > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > @@ -928,6 +928,53 @@ static int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of, > return ret; > } > > +static ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, > + char *buf, size_t nbytes, loff_t off) > +{ > + struct rdt_resource *r = of->kn->parent->priv; > + int ret = 0; > + bool enable; > + > + /* Valid input requires a trailing newline */ > + if (nbytes == 0 || buf[nbytes - 1] != '\n') > + return -EINVAL; > + > + buf[nbytes - 1] = '\0'; > + > + cpus_read_lock(); > + mutex_lock(&rdtgroup_mutex); > + > + rdt_last_cmd_clear(); > + > + if (!strcmp(buf, "default")) { > + enable = 0; > + } else if (!strcmp(buf, "mbm_cntr_assign")) { > + if (r->mon.mbm_cntr_assignable) { > + enable = 1; > + } else { > + ret = -EINVAL; > + rdt_last_cmd_puts("mbm_cntr_assign mode is not supported\n"); > + goto write_exit; > + } > + } else { > + ret = -EINVAL; > + rdt_last_cmd_puts("Unsupported assign mode\n"); > + goto write_exit; > + } > + > + if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) { > + ret = resctrl_arch_mbm_cntr_assign_set(r, enable); > + if (!ret) > + mbm_cntr_reset(r); The following APIs interact with the MBM assignable counters: mbm_cntr_alloc() mbm_cntr_get() mbm_cntr_free() mbm_cntr_reset() appears to be related but does significantly more than interact with the MBM assignable counters and that creates a confusing API. How about introducing mbm_cntr_free_all() that _only_ releases all MBM assignable counters and match with mbm_cntr_free() that releases a single MBM assignable counter? mbm_cntr_free_all() lives with the other functions operating on MBM assignable counters, thus not hiding its functionality in other parts of resctrl. This series open codes reset of non-architectural state in two places, within mbm_cntr_reset() and within mbm_config_write_domain(). That can be turned into a new helper that only resets architectural state, for example resctrl_reset_rmid_all() to match existing resctrl_arch_reset_rmid_all(). resctrl_arch_mbm_cntr_assign_set() can also reset any architectural state leaving mbm_cntr_free_all() and resctrl_reset_rmid_all() to be called here and from within mbm_config_write_domain(). What do you think? > + } > + > +write_exit: > + mutex_unlock(&rdtgroup_mutex); > + cpus_read_unlock(); > + > + return ret ?: nbytes; > +} > + > #ifdef CONFIG_PROC_CPU_RESCTRL > > /* > @@ -1945,9 +1992,10 @@ static struct rftype res_common_files[] = { > }, > { > .name = "mbm_assign_mode", > - .mode = 0444, > + .mode = 0644, > .kf_ops = &rdtgroup_kf_single_ops, > .seq_show = resctrl_mbm_assign_mode_show, > + .write = resctrl_mbm_assign_mode_write, > .fflags = RFTYPE_MON_INFO, > }, > { Reinette