Hey Rob, thanks for the review.
Rob Herring <robh@xxxxxxxxxx> writes:
On Mon, Jan 27, 2025 at 4:26 PM Colton Lewis <coltonlewis@xxxxxxxxxx>
wrote:
@@ -1215,10 +1243,19 @@ static void __armv8pmu_probe_pmu(void *info)
cpu_pmu->pmuver = pmuver;
probe->present = true;
+ pmcr_n = FIELD_GET(ARMV8_PMU_PMCR_N, armv8pmu_pmcr_read());
/* Read the nb of CNTx counters supported from PMNC */
- bitmap_set(cpu_pmu->cntr_mask,
- 0, FIELD_GET(ARMV8_PMU_PMCR_N, armv8pmu_pmcr_read()));
+ bitmap_set(cpu_pmu->cntr_mask, 0, pmcr_n);
+
+ if (reserved_guest_counters > 0 && reserved_guest_counters <
pmcr_n) {
+ cpu_pmu->hpmn = reserved_guest_counters;
+ cpu_pmu->partitioned = true;
You're storing the same information 3 times. 'partitioned' is just
'reserved_guest_counters != 0' or 'cpu_pmu->hpmn != pmcr_n'.
Yes, because code outside this module that isn't already reading PMCR.N
will need to know the result of that comparion.
+ } else {
+ reserved_guest_counters = 0;
+ cpu_pmu->hpmn = pmcr_n;
+ cpu_pmu->partitioned = false;
+ }
/* Add the CPU cycles counter */
set_bit(ARMV8_PMU_CYCLE_IDX, cpu_pmu->cntr_mask);
@@ -1516,3 +1553,5 @@ void arch_perf_update_userpage(struct perf_event
*event,
userpg->cap_user_time_zero = 1;
userpg->cap_user_time_short = 1;
}
+
+module_param(reserved_guest_counters, byte, 0);
Module params are generally discouraged. Since this driver can't be a
module, this is a boot time only option. There's little reason this
can't be a sysfs setting. There's some complexity in changing this
when counters are in use (just reject the change) and when we have
asymmetric PMUs. Alternatively, it could be a sysctl like user access.
I see what you mean. I'm not dealing with those complexities yet. That's
why this is an RFC.
Rob
