Hi Reinette,
On 2/6/25 12:05, Reinette Chatre wrote:
> Hi Babu,
>
> On 1/22/25 12:20 PM, Babu Moger wrote:
>> Resctrl subsystem can support two monitoring modes, 'mbm_cntr_assign' or
>> 'default'. 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 <babu.moger@xxxxxxx>
>> ---
>
>
>> ---
>> 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.
ok. Will change it to 'Unassigned'.
>
>> +
>> + 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:
This sounds (monitoring mode) better.
> 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?
Sounds like a good code separation. It should be fine.
Will let you know if there are any issues.
>
>> + }
>> +
>> +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
>
--
Thanks
Babu Moger
