Hey Rob, thanks for the review.
Rob Herring robh@kernel.org writes:
On Mon, Jan 27, 2025 at 4:26 PM Colton Lewis coltonlewis@google.com 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