Hi Reinette,
On 12/19/2024 5:59 PM, Reinette Chatre wrote:
Hi Babu,
On 12/12/24 12:15 PM, Babu Moger wrote:
In mbm_cntr_assign mode, the hardware counter should be assigned to read
the MBM events.
Report 'Unassigned' in case the user attempts to read the events without
assigning the counter.
Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
..
diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index c075fcee96b7..3ec14c314606 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -430,6 +430,16 @@ When monitoring is enabled all MON groups will also contain:
for the L3 cache they occupy). These are named "mon_sub_L3_YY"
where "YY" is the node number.
+ When supported the mbm_cntr_assign mode allows users to assign a
"When supported" -> "When enabled"? Or perhaps just drop that and start with
"mbm_cntr_assign mode allows users ..."
ok.
+ counter to mon_hw_id, event pair enabling bandwidth monitoring for
+ as long as the counter remains assigned. The hardware will continue
+ tracking the assigned mon_hw_id until the user manually unassigns
+ it, ensuring that counters are not reset during this period. With
+ a limited number of counters, the system may run out of assignable
+ counters. In that case, MBM event counters will return 'Unassigned'
+ when the event is read. Users must manually assign a counter to read
+ the events.
+
"mon_hw_id":
Available only with debug option. The identifier used by hardware
for the monitor group. On x86 this is the RMID.
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 200d89a64027..8e265a86e524 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -527,6 +527,12 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
/* When picking a CPU from cpu_mask, ensure it can't race with cpuhp */
lockdep_assert_cpus_held();
+ if (resctrl_arch_mbm_cntr_assign_enabled(r) && is_mbm_event(evtid) &&
+ !mbm_cntr_assigned(r, d, rdtgrp, evtid)) {
+ rr->err = -ENOENT;
+ return;
+ }
+
hmmm ... d can be NULL here after the SNC support. Since the file that needs a
sum is essentially software backed I do not think assigning counters would
apply to it (but it may theoretically apply to the domains it consists of).
I think it may be safer to just move this check into rdtgroup_mondata_show()
where it reads data for a single domain.
Sure.
I am not sure if we need to change the documentation because of this. One option
could be a rewording to "MBM event counters may return 'Unassigned' or
'Unavailable' when the event is read".
ok.
Thanks
Babu
