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Message-ID: <e45064ca-56f5-4d86-b088-cd24ffc0e96d@amd.com> Date: Tue, 15 Jul 2025 09:16:52 -0500 From: "Moger, Babu" <babu.moger@....com> To: Peter Newman <peternewman@...gle.com> Cc: corbet@....net, tony.luck@...el.com, reinette.chatre@...el.com, james.morse@....com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, Dave.Martin@....com, x86@...nel.org, hpa@...or.com, akpm@...ux-foundation.org, paulmck@...nel.org, rostedt@...dmis.org, Neeraj.Upadhyay@....com, david@...hat.com, arnd@...db.de, fvdl@...gle.com, seanjc@...gle.com, jpoimboe@...nel.org, pawan.kumar.gupta@...ux.intel.com, xin@...or.com, manali.shukla@....com, tao1.su@...ux.intel.com, sohil.mehta@...el.com, kai.huang@...el.com, xiaoyao.li@...el.com, peterz@...radead.org, xin3.li@...el.com, kan.liang@...ux.intel.com, mario.limonciello@....com, thomas.lendacky@....com, perry.yuan@....com, gautham.shenoy@....com, chang.seok.bae@...el.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, eranian@...gle.com Subject: Re: [PATCH v15 05/34] x86/cpufeatures: Add support for Assignable Bandwidth Monitoring Counters (ABMC) Hi Peter, On 7/15/25 06:47, Peter Newman wrote: > Hi Babu, > > On Wed, Jul 9, 2025 at 12:18 AM Babu Moger <babu.moger@....com> wrote: >> >> Users can create as many monitor groups as RMIDs supported by the hardware. >> However, bandwidth monitoring feature on AMD system only guarantees that >> RMIDs currently assigned to a processor will be tracked by hardware. The >> counters of any other RMIDs which are no longer being tracked will be reset >> to zero. The MBM event counters return "Unavailable" for the RMIDs that are >> not tracked by hardware. So, there can be only limited number of groups >> that can give guaranteed monitoring numbers. With ever changing >> configurations there is no way to definitely know which of these groups are >> being tracked during a particular time. Users do not have the option to >> monitor a group or set of groups for a certain period of time without >> worrying about RMID being reset in between. >> >> The ABMC feature allows users to assign a hardware counter to an RMID, >> event pair and monitor bandwidth usage as long as it is assigned. The >> hardware continues to track the assigned counter until it is explicitly >> unassigned by the user. There is no need to worry about counters being >> reset during this period. Additionally, the user can specify the type of >> memory transactions (e.g., reads, writes) for the counter to track. >> >> Without ABMC enabled, monitoring will work in current mode without >> assignment option. >> >> The Linux resctrl subsystem provides an interface that allows monitoring of >> up to two memory bandwidth events per group, selected from a combination of >> available total and local events. When ABMC is enabled, two events will be >> assigned to each group by default, in line with the current interface >> design. Users will also have the option to configure which types of memory >> transactions are counted by these events. >> >> Due to the limited number of available counters (32), users may quickly >> exhaust the available counters. If the system runs out of assignable ABMC >> counters, the kernel will report an error. In such cases, users will need >> to unassign one or more active counters to free up counters for new >> assignments. resctrl will provide options to assign or unassign events >> through the group-specific interface file. >> >> The feature is detected via CPUID_Fn80000020_EBX_x00 bit 5. >> Bits Description >> 5 ABMC (Assignable Bandwidth Monitoring Counters) >> >> The feature details are documented in APM listed below [1]. >> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming >> Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable Bandwidth >> Monitoring (ABMC). >> >> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 >> Signed-off-by: Babu Moger <babu.moger@....com> >> --- >> Note: Checkpatch checks/warnings are ignored to maintain coding style. >> >> v15: Minor changelog update. >> >> v14: Removed the dependancy on X86_FEATURE_CQM_MBM_TOTAL and X86_FEATURE_CQM_MBM_LOCAL. >> as discussed in https://lore.kernel.org/lkml/5f8b21c6-5166-46a6-be14-0c7c9bfb7cde@intel.com/ >> Need to re-work on ABMC enumeration during the init. >> Updated changelog with few text update. >> >> v13: Updated the commit log with Linux interface details. >> >> v12: Removed the dependancy on X86_FEATURE_BMEC. >> Removed the Reviewed-by tag as patch has changed. >> >> v11: No changes. >> >> v10: No changes. >> >> v9: Took care of couple of minor merge conflicts. No other changes. >> >> v8: No changes. >> >> v7: Removed "" from feature flags. Not required anymore. >> https://lore.kernel.org/lkml/20240817145058.GCZsC40neU4wkPXeVR@fat_crate.local/ >> >> v6: Added Reinette's Reviewed-by. Moved the Checkpatch note below ---. >> >> v5: Minor rebase change and subject line update. >> >> v4: Changes because of rebase. Feature word 21 has few more additions now. >> Changed the text to "tracked by hardware" instead of active. >> >> v3: Change because of rebase. Actual patch did not change. >> >> v2: Added dependency on X86_FEATURE_BMEC. >> --- >> arch/x86/include/asm/cpufeatures.h | 1 + >> arch/x86/kernel/cpu/scattered.c | 1 + >> 2 files changed, 2 insertions(+) >> >> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h >> index b78af55aa22e..d2950a0177cd 100644 >> --- a/arch/x86/include/asm/cpufeatures.h >> +++ b/arch/x86/include/asm/cpufeatures.h >> @@ -490,6 +490,7 @@ >> #define X86_FEATURE_PREFER_YMM (21*32+ 8) /* Avoid ZMM registers due to downclocking */ >> #define X86_FEATURE_APX (21*32+ 9) /* Advanced Performance Extensions */ >> #define X86_FEATURE_INDIRECT_THUNK_ITS (21*32+10) /* Use thunk for indirect branches in lower half of cacheline */ >> +#define X86_FEATURE_ABMC (21*32+11) /* Assignable Bandwidth Monitoring Counters */ > > It looks like this bit has been taken by X86_FEATURE_TSA_SQ_NO. I had > to move X86_FEATURE_ABMC down to (21*32+14) on tip/master. > Yea. Thats right. Will take care in next revision. -- Thanks Babu Moger
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