linux-kernel - Re: [PATCH v2 11/33] x86/intel_rdt: Hot cpu support for Cache Allocation

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Message-ID: <alpine.DEB.2.20.1609081154230.5647@nanos>
Date:   Thu, 8 Sep 2016 12:03:02 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
cc:     "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>, Borislav Petkov <bp@...e.de>,
        Stephane Eranian <eranian@...gle.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Shaohua Li <shli@...com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        Sai Prakhya <sai.praneeth.prakhya@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2 11/33] x86/intel_rdt: Hot cpu support for Cache
 Allocation

On Thu, 8 Sep 2016, Fenghua Yu wrote:
> +/*
> + * cbm_update_msrs() - Updates all the existing IA32_L3_MASK_n MSRs
> + * which are one per CLOSid on the current package.
> + */
> +static void cbm_update_msrs(void *dummy)
> +{
> +	int maxid = boot_cpu_data.x86_cache_max_closid;
> +	struct rdt_remote_data info;
> +	unsigned int i;
> +
> +	for (i = 0; i < maxid; i++) {
> +		if (cctable[i].clos_refcnt) {
> +			info.msr = CBM_FROM_INDEX(i);
> +			info.val = cctable[i].cbm;
> +			msr_cpu_update(&info);
> +		}
> +	}
> +}
> +
> +static int intel_rdt_online_cpu(unsigned int cpu)
> +{
> +	struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
> +
> +	state->closid = 0;
> +	mutex_lock(&rdtgroup_mutex);
> +	/* The cpu is set in root rdtgroup after online. */
> +	cpumask_set_cpu(cpu, &root_rdtgrp->cpu_mask);
> +	per_cpu(cpu_rdtgroup, cpu) = root_rdtgrp;
> +	/*
> +	 * If the cpu is first time found and set in its siblings that

-ENOPARSE

> +	 * share the same cache, update the CBM MSRs for the cache.
> +	 */
> +	if (rdt_cpumask_update(cpu))
> +		smp_call_function_single(cpu, cbm_update_msrs, NULL, 1);

This smp_call_function() is a pointless exercise. online callbacks are
guaranteed to run on @cpu.

> +	mutex_unlock(&rdtgroup_mutex);
> +}
> +
> +static int clear_rdtgroup_cpumask(unsigned int cpu)
> +{
> +	struct list_head *l;
> +	struct rdtgroup *r;
> +
> +	list_for_each(l, &rdtgroup_lists) {
> +		r = list_entry(l, struct rdtgroup, rdtgroup_list);
> +		if (cpumask_test_cpu(cpu, &r->cpu_mask)) {
> +			cpumask_clear_cpu(cpu, &r->cpu_mask);
> +			return 0;
> +		}
> +	}
> +
> +	return -EINVAL;

What's the point of the return value if it gets ignored anyway.

> +}
> +
> +static int intel_rdt_offline_cpu(unsigned int cpu)
> +{
> +	int i;
> +
> +	mutex_lock(&rdtgroup_mutex);
> +	if (!cpumask_test_and_clear_cpu(cpu, &rdt_cpumask)) {
> +		mutex_unlock(&rdtgroup_mutex);
> +		return;
> +	}
> +
> +	cpumask_and(&tmp_cpumask, topology_core_cpumask(cpu), cpu_online_mask);
> +	cpumask_clear_cpu(cpu, &tmp_cpumask);
> +	i = cpumask_any(&tmp_cpumask);
> +
> +	if (i < nr_cpu_ids)
> +		cpumask_set_cpu(i, &rdt_cpumask);
> +
> +	clear_rdtgroup_cpumask(cpu);
> +	mutex_unlock(&rdtgroup_mutex);
> +}
> +
>  static int __init intel_rdt_late_init(void)
>  {
>  	struct cpuinfo_x86 *c = &boot_cpu_data;
> @@ -169,6 +247,13 @@ static int __init intel_rdt_late_init(void)
>  
>  	for_each_online_cpu(i)
>  		rdt_cpumask_update(i);
> +
> +	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> +				"AP_INTEL_RDT_ONLINE",
> +				intel_rdt_online_cpu, intel_rdt_offline_cpu);

Why are you using nocalls() here? cpuhp_setup_state() will invoke
intel_rdt_online_cpu() on every online cpu.

And you just call rdt_cpumask_update() for each cpu. What is doing the rest
of the cpu initialization (cpu_rdtgroup, root_rtgroup->cpu_mask) ????

> +	if (err < 0)
> +		goto out_err;

Oh well.....

Thanks,

	tglx