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Tue, 13 May 2025 03:19:35 +0000 Message-ID: Date: Tue, 13 May 2025 11:19:23 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 12/31] fs/resctrl: Improve handling for events that can be read from any CPU To: Tony Luck , Reinette Chatre CC: , , , Fenghua Yu , "Maciej Wieczor-Retman" , Peter Newman , Babu Moger , Anil Keshavamurthy , Dave Martin , "James Morse" , Drew Fustini References: <20250429003359.375508-1-tony.luck@intel.com> <20250429003359.375508-13-tony.luck@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <20250429003359.375508-13-tony.luck@intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SI1PR02CA0057.apcprd02.prod.outlook.com (2603:1096:4:1f5::10) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|MN2PR11MB4693:EE_ X-MS-Office365-Filtering-Correlation-Id: e16b253d-361d-4026-0eff-08dd91ccfc29 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024; 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This was true for x86 events accessed with an MSR interface, > but may not be true for other access methods such as MMIO. > > Add a flag to each instance of struct mon_evt that can be set by > architecture code to indicate there is no restriction on which > CPU can read the event counter. > > Change struct mon_data and struct rmid_read to have a pointer to > the struct mon_evt instead of the event id. > > Add an extra argument to resctrl_enable_mon_event() so architecture > code can indicate which events can be read on any CPU when enabling > the event. > > Bypass all the smp_call*() code for events that can be read on any CPU > and call mon_event_count() directly from mon_event_read(). > > Skip checks in __mon_event_count() that the read is being done from > a CPU in the correct domain or cache scope. > Since __mon_event_count() was supposed to run in atomic context, the smp_processor_id() would not report any warning previously. After this change, if the evt->any_cpu is true, we read the telemetry counter directly without IPI involved and in non-atomic context, we might get warning like below: BUG: using smp_processor_id() in preemptible [00000000] code: mount/1595 caller is __mon_event_count+0x2e/0x1e0 2483 [ 2095.332850] Call Trace: 2484 [ 2095.332861] 2485 [ 2095.332872] dump_stack_lvl+0x55/0x70 2486 [ 2095.332887] check_preemption_disabled+0xbf/0xe0 2487 [ 2095.332902] __mon_event_count+0x2e/0x1e0 2488 [ 2095.332918] mon_event_count+0x2a/0xa0 2489 [ 2095.332934] mon_add_all_files+0x202/0x270 2490 [ 2095.332953] mkdir_mondata_subdir+0x1bf/0x1e0 2491 [ 2095.332970] ? kcore_update_ram.isra.0+0x270/0x270 2492 [ 2095.332985] mkdir_mondata_all+0x9d/0x100 2493 [ 2095.333000] rdt_get_tree+0x336/0x5d0 2494 [ 2095.333014] vfs_get_tree+0x26/0xf0 2495 [ 2095.333028] do_new_mount+0x186/0x350 2496 [ 2095.333044] __x64_sys_mount+0x101/0x130 2497 [ 2095.333061] do_syscall_64+0x54/0xd70 2498 [ 2095.333075] entry_SYSCALL_64_after_hwframe+0x76/0x7e Maybe avoid getting the CPU at all in __mon_event_count() if evt->any_cpu is true? thanks, Chenyu diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c index d9364bee486e..32385c811a92 100644 --- a/fs/resctrl/monitor.c +++ b/fs/resctrl/monitor.c @@ -358,12 +358,15 @@ static struct mbm_state *get_mbm_state(struct rdt_l3_mon_domain *d, u32 closid, static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr) { - int cpu = smp_processor_id(); struct rdt_l3_mon_domain *d; struct mbm_state *m; - int err, ret; + int err, ret, cpu; u64 tval = 0; + /*only CPU sensitive event read cares about which CPU to read from */ + if (!rr->evt->any_cpu) + cpu = smp_processor_id(); tele