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SubjectRe: [PATCH 8/9] x86/intel_rdt: Hot cpu support for Cache Allocation


On Wed, 29 Jul 2015, Peter Zijlstra wrote:

> On Wed, Jul 01, 2015 at 03:21:09PM -0700, Vikas Shivappa wrote:
>> +/*
>> + * cbm_update_msrs() - Updates all the existing IA32_L3_MASK_n MSRs
>> + * which are one per CLOSid except IA32_L3_MASK_0 on the current package.
>> + */
>> +static void cbm_update_msrs(void *info)
>> +{
>> + int maxid = boot_cpu_data.x86_cache_max_closid;
>> + unsigned int i;
>> +
>> + /*
>> + * At cpureset, all bits of IA32_L3_MASK_n are set.
>> + * The index starts from one as there is no need
>> + * to update IA32_L3_MASK_0 as it belongs to root cgroup
>> + * whose cache mask is all 1s always.
>> + */
>> + for (i = 1; i < maxid; i++) {
>> + if (ccmap[i].clos_refcnt)
>> + cbm_cpu_update((void *)i);
>> + }
>> +}
>> +
>> +static inline void intel_rdt_cpu_start(int cpu)
>> +{
>> + struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
>> +
>> + state->closid = 0;
>> + mutex_lock(&rdt_group_mutex);
>> + if (rdt_cpumask_update(cpu))
>> + smp_call_function_single(cpu, cbm_update_msrs, NULL, 1);
>> + mutex_unlock(&rdt_group_mutex);
>> +}
>
> If you were to guard your array with both a mutex and a raw_spinlock
> then you can avoid the IPI and use CPU_STARTING.

Cpu_online was just good enough as the tasks would be ready to be scheduled. iow
, its just at the right time.

could avoid using the interrupt disabled time ?
Dont really need the *interrupt disabled* cpu_starting notification - can leave
that for more important code/lock free code can go there. or this change should
not be a big concern ?

>
>> +static int intel_rdt_cpu_notifier(struct notifier_block *nb,
>> + unsigned long action, void *hcpu)
>> +{
>> + unsigned int cpu = (unsigned long)hcpu;
>> +
>> + switch (action) {
>> + case CPU_DOWN_FAILED:
>> + case CPU_ONLINE:
>> + intel_rdt_cpu_start(cpu);
>> + break;
>> + case CPU_DOWN_PREPARE:
>> + intel_rdt_cpu_exit(cpu);
>> + break;
>> + default:
>> + break;
>> + }
>> +
>> + return NOTIFY_OK;
>> }
>


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