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Message-ID: <5005f017-a499-43e8-ab3d-cddf7c9d8053@amd.com>
Date: Tue, 16 Jul 2024 11:51:13 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
fenghua.yu@...el.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org,
tj@...nel.org, peterz@...radead.org, yanjiewtw@...il.com,
kim.phillips@....com, lukas.bulwahn@...il.com, seanjc@...gle.com,
jmattson@...gle.com, leitao@...ian.org, jpoimboe@...nel.org,
rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com,
jithu.joseph@...el.com, kai.huang@...el.com, kan.liang@...ux.intel.com,
daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, eranian@...gle.com, james.morse@....com
Subject: Re: [PATCH v5 07/20] x86/resctrl: Introduce the interface to display
monitor mode
Hi Reinette,
On 7/12/24 17:06, Reinette Chatre wrote:
> Hi Babu,
>
> On 7/3/24 2:48 PM, Babu Moger wrote:
>> The ABMC feature provides an option to the user to assign a hardware
>> counter to an RMID and monitor the bandwidth as long as it is assigned.
>> ABMC mode is enabled by default when supported. System can be one mode
>> at a time (Legacy monitor mode or ABMC mode).
>>
>> Provide an interface to display the monitor mode on the system.
>> $cat /sys/fs/resctrl/info/L3_MON/mbm_mode
>> [abmc]
>> legacy
>
> <insert snippet about what happens when user switches from one mode
> to another>
Sure.
>
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
>> v5: Changed interface name to mbm_mode.
>> It will be always available even if ABMC feature is not supported.
>> Added description in resctrl.rst about ABMC mode.
>> Fixed display abmc and legacy consistantly.
>>
>> v4: Fixed the checks for legacy and abmc mode. Default it ABMC.
>>
>> v3: New patch to display ABMC capability.
>> ---
>> Documentation/arch/x86/resctrl.rst | 30 ++++++++++++++++++++++++++
>> arch/x86/kernel/cpu/resctrl/monitor.c | 2 ++
>> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 26 ++++++++++++++++++++++
>> 3 files changed, 58 insertions(+)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst
>> b/Documentation/arch/x86/resctrl.rst
>> index 30586728a4cd..108e494fd7cc 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -257,6 +257,36 @@ with the following files:
>> # cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config
>> 0=0x30;1=0x30;3=0x15;4=0x15
>> +"mbm_mode":
>> + Reports the list of assignable monitoring features supported. The
>> + enclosed brackets indicate which feature is enabled.
>> + ::
>> +
>> + cat /sys/fs/resctrl/info/L3_MON/mbm_mode
>> + [abmc]
>> + legacy
>> +
>
> "mbm_cntr" mode can be documented here with the details on how AMD's ABMC is
> one example of how it may be implemented on a system.
Will display as "mbm_cntr_assignable".
Yes. Will add details specific about AMD's ABMC.
>
>> + The 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 for certain
>> + point of time. Users do not have the option to monitor a group or
>> + set of groups for certain period of time without worrying about
>> + RMID being reset in between.
>> +
>> + The ABMC feature provides an option to the user to assign a
>> + hardware counter to an RMID and monitor the bandwidth as long as
>> + it is assigned. The assigned RMID will be tracked by the hardware
>> + until the user unassigns it manually. There is no need to worry
>> + about counters being reset during this period.
>> +
>> + Without ABMC enabled, monitoring will work in "legacy" mode
>> + without assignment option.
>
> Let "legacy" be a distinct mode, instead of an alternative to ABMC.
Will add as another mode.
>
>> +
>> "max_threshold_occupancy":
>> Read/write file provides the largest value (in
>> bytes) at which a previously used LLC_occupancy
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 12793762ca24..6c4cb36b4b50 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -1245,6 +1245,8 @@ int __init rdt_get_mon_l3_config(struct
>> rdt_resource *r)
>> }
>> }
>> + resctrl_file_fflags_init("mbm_mode", RFTYPE_MON_INFO);
>> +
>
> Is this special flag assignment necessary? With file always visible I
> think it
> can just be initialized in res_common_files below with the flag already
> assigned?
Yes. We can do that.
>
>> l3_mon_evt_init(r);
>> r->mon_capable = true;
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 471fc0dbd7c3..3988d7b86817 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -845,6 +845,26 @@ static int rdtgroup_rmid_show(struct
>> kernfs_open_file *of,
>> return ret;
>> }
>> +static int rdtgroup_mbm_mode_show(struct kernfs_open_file *of,
>> + struct seq_file *s, void *v)
>> +{
>> + struct rdt_resource *r = of->kn->parent->priv;
>> +
>> + if (r->mon.abmc_capable) {
>> + if (resctrl_arch_get_abmc_enabled()) {
>> + seq_puts(s, "[abmc]\n");
>> + seq_puts(s, "legacy\n");
>> + } else {
>> + seq_puts(s, "abmc\n");
>> + seq_puts(s, "[legacy]\n");
>> + }
>> + } else {
>> + seq_puts(s, "[legacy]\n");
>> + }
>> +
>> + return 0;
>> +}
>> +
>> #ifdef CONFIG_PROC_CPU_RESCTRL
>> /*
>> @@ -1901,6 +1921,12 @@ static struct rftype res_common_files[] = {
>> .seq_show = mbm_local_bytes_config_show,
>> .write = mbm_local_bytes_config_write,
>> },
>> + {
>> + .name = "mbm_mode",
>> + .mode = 0444,
>> + .kf_ops = &rdtgroup_kf_single_ops,
>> + .seq_show = rdtgroup_mbm_mode_show,
>> + },
>> {
>> .name = "cpus",
>> .mode = 0644,
>
> Reinette
>
--
Thanks
Babu Moger
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