Re: [PATCH v4 11/13] x86/resctrl: Add sysfs interface to write the event configuration

Moger, Babu
2022-09-19T16:52:04Z

On 9/16/22 11:17, Reinette Chatre wrote:
> Hi Babu,
>
> On 9/7/2022 11:01 AM, Babu Moger wrote:
>
> ...
>
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 6f067c1ac7c1..59b484eb1267 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -330,9 +330,121 @@ int rdtgroup_mondata_config_show(struct seq_file *m, void *arg)
>> return ret;
>> }
>>
>> +/*
>> + * This is called via IPI to read the CQM/MBM counters
>> + * in a domain.
> copy&paste from previous patch?
Will correct it.
>
>> + */
>> +void mon_event_config_write(void *info)
>> +{
>> + struct mon_config_info *mon_info = info;
>> + u32 msr_index;
>> +
>> + switch (mon_info->evtid) {
>> + case QOS_L3_MBM_TOTAL_EVENT_ID:
>> + msr_index = 0;
>> + break;
>> + case QOS_L3_MBM_LOCAL_EVENT_ID:
>> + msr_index = 1;
>> + break;
>> + default:
>> + /* Not expected to come here */
>> + return;
>> + }
>> +
>> + wrmsr(MSR_IA32_EVT_CFG_BASE + msr_index, mon_info->mon_config, 0);
>> +}
>> +
>> +ssize_t rdtgroup_mondata_config_write(struct kernfs_open_file *of,
>> + char *buf, size_t nbytes, loff_t off)
>> +{
>> + struct mon_config_info mon_info;
>> + struct rdt_hw_resource *hw_res;
>> + struct rdtgroup *rdtgrp;
>> + struct rdt_resource *r;
>> + unsigned int mon_config;
>> + cpumask_var_t cpu_mask;
>> + union mon_data_bits md;
>> + struct rdt_domain *d;
>> + u32 resid, domid;
>> + int ret = 0, cpu;
>> +
>> + ret = kstrtouint(buf, 0, &mon_config);
>> + if (ret)
>> + return ret;
>> +
>> + rdt_last_cmd_clear();
>> +
>> + /* mon_config cannot be more than the supported set of events */
>> + if (mon_config > MAX_EVT_CONFIG_BITS) {
>> + rdt_last_cmd_puts("Invalid event configuration\n");
>> + return -EINVAL;
>> + }
>> +
>> + cpus_read_lock();
>> + rdtgrp = rdtgroup_kn_lock_live(of->kn);
>> + if (!rdtgrp) {
>> + return -ENOENT;
>> + goto e_unlock;
>> + }
>> +
>> + if (!zalloc_cpumask_var(&cpu_mask, GFP_KERNEL)) {
>> + ret = -ENOMEM;
>> + goto e_unlock;
>> + }
>> +
>> + md.priv = of->kn->priv;
>> + resid = md.u.rid;
>> + domid = md.u.domid;
>> +
>> + hw_res = &rdt_resources_all[resid];
>> + r = &hw_res->r_resctrl;
>> + d = rdt_find_domain(r, domid, NULL);
>> + if (IS_ERR_OR_NULL(d)) {
>> + ret = -ENOENT;
>> + goto e_cpumask;
>> + }
>> +
>> + /*
>> + * Read the current config value first. If both are same
>> + * then we dont need to write again
>> + */
>> + mon_info.evtid = md.u.evtid;
>> + mondata_config_read(d, &mon_info);
>> + if (mon_info.mon_config == mon_config)
>> + goto e_cpumask;
>> +
>> + mon_info.mon_config = mon_config;
>> +
>> + /* Pick all the CPUs in the domain instance */
>> + for_each_cpu(cpu, &d->cpu_mask)
>> + cpumask_set_cpu(cpu, cpu_mask);
>> +
>> + /* Update MSR_IA32_EVT_CFG_BASE MSR on all the CPUs in cpu_mask */
>> + on_each_cpu_mask(cpu_mask, mon_event_config_write, &mon_info, 1);
> If this is required then could you please add a comment why every CPU in
> the domain needs to be updated? Until now configuration changes
> only needed to be made on one CPU per domain.
> Even in the previous patch when the user reads the current configuration
> value it is only done on one CPU in the domain ... to me that implies
> that the scope is per domain and only one CPU in the domain needs to be
> changed.

Yes, This register is domain specific. However the hardware team
recommends it to update on all the CPU threads. It is not clear in the
specs right now.

I have asked them to make that clear in the specs next time.

>
>> +
>> + /*
>> + * When an Event Configuration is changed, the bandwidth counters
>> + * for all RMIDs and Events will be cleared, and the U-bit for every
>> + * RMID will be set on the next read to any BwEvent for every RMID.
>> + * Clear the mbm_local and mbm_total counts for all the RMIDs.
>> + */
> This is a snippet that was copied from the hardware spec and since it is
> inserted into the kernel driver the context makes it hard to understand.
> Could it be translated into what it means in this context?
> Perhaps something like:
>
> /*
> * When an Event Configuration is changed, the bandwidth counters
> * for all RMIDs and Events will be cleared by the hardware. The
> * hardware also sets MSR_IA32_QM_CTR.Unavailable (bit 62) for every
> * RMID on the next read to any event for every RMID. Subsequent
> * reads will have MSR_IA32_QM_CTR.Unavailable (bit 62) cleared
> * while it is tracked by the hardware.
> * Clear the mbm_local and mbm_total counts for all the RMIDs.
> */
>
> Please fixup where I got it wrong.

Looks good.

Thanks Babu

>
>> + memset(d->mbm_local, 0, sizeof(struct mbm_state) * r->num_rmid);
>> + memset(d->mbm_total, 0, sizeof(struct mbm_state) * r->num_rmid);
>> +
> Reinette

--
Thanks
Babu Moger