Messages in this thread | | | Date | Fri, 31 Jul 2015 16:21:19 -0700 (PDT) | From | Vikas Shivappa <> | Subject | Re: [PATCH 8/9] x86/intel_rdt: Hot cpu support for Cache Allocation |
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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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