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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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