linux-kernel - Re: [PATCH 09/10] x86/intel_rdt: Hot cpu support for Cache Allocation

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Message-ID: <alpine.DEB.2.10.1506241413360.32420@vshiva-Udesk>
Date:	Wed, 24 Jun 2015 14:15:47 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
	mingo@...nel.org, tj@...nel.org, peterz@...radead.org,
	Matt Fleming <matt.fleming@...el.com>,
	"Auld, Will" <will.auld@...el.com>,
	"Williamson, Glenn P" <glenn.p.williamson@...el.com>,
	"Juvva, Kanaka D" <kanaka.d.juvva@...el.com>,
	"Autee, Priya V" <priya.v.autee@...el.com>
Subject: Re: [PATCH 09/10] x86/intel_rdt: Hot cpu support for Cache
 Allocation



On Wed, 24 Jun 2015, Thomas Gleixner wrote:

> On Tue, 23 Jun 2015, 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 inline void cbm_update_msrs(void)
>> +{
>> +	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);
>
> So this is called via
>
>   intel_rdt_cpu_notifier(CPU_ONLINE)
>     intel_rdt_cpu_start()
>       cbm_update_msrs()
> 	 cbm_cpu_update()
> 	   wrmsr()
>
> And runs on the CPU which initiated the hotplug and not on the newly
> online cpu. Pretty useless, right?

Will fix.

>
>> +	}
>> +}
>> +
>> +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))
>> +		cbm_update_msrs();
>> +	mutex_unlock(&rdt_group_mutex);
>> +}
>> +
>> +static void intel_rdt_cpu_exit(unsigned int cpu)
>> +{
>> +	int i;
>> +
>> +	mutex_lock(&rdt_group_mutex);
>> +	if (!cpumask_test_and_clear_cpu(cpu, &rdt_cpumask)) {
>> +		mutex_unlock(&rdt_group_mutex);
>> +		return;
>> +	}
>> +
>> +	i = cpumask_any_online_but(topology_core_cpumask(cpu), cpu);
>> +	if (i < nr_cpu_ids)
>> +		cpumask_set_cpu(i, &rdt_cpumask);
>> +	mutex_unlock(&rdt_group_mutex);
>
> Same issue as in the cqm patch.

will fix.
yes this may risk the package to not have some updates.

Thanks,
Vikas

>
> Thanks,
>
> 	tglx
>
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