linux-kernel - Re: [PATCH 5/5] x86/intel_rdt: hotcpu updates for RDT

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Date:   Thu, 30 Mar 2017 12:03:44 -0700 (PDT)
From:   Shivappa Vikas <vikas.shivappa@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
cc:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        vikas.shivappa@...el.com, linux-kernel@...r.kernel.org,
        x86@...nel.org, hpa@...or.com, mingo@...nel.org,
        peterz@...radead.org, ravi.v.shankar@...el.com,
        tony.luck@...el.com, fenghua.yu@...el.com, andi.kleen@...el.com
Subject: Re: [PATCH 5/5] x86/intel_rdt: hotcpu updates for RDT



On Wed, 1 Mar 2017, Thomas Gleixner wrote:

>>  	WARN_ON(c->x86_cache_occ_scale != cqm_l3_scale);
>>
>> @@ -1585,12 +1580,17 @@ static int intel_cqm_cpu_starting(unsigned int cpu)
>>
>>  static int intel_cqm_cpu_exit(unsigned int cpu)
>>  {
>> +	struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
>
> Can be this_cpu_ptr() because the callback is guaranteed to run on the
> outgoing CPU.

Will fix this. Assumed the calls are setup cache alloc way - 
cpuhp_setup_state(CPUHP_AP_ONLINE_DYN ..

>
>>  	int target;
>>
>>  	/* Is @cpu the current cqm reader for this package ? */
>>  	if (!cpumask_test_and_clear_cpu(cpu, &cqm_cpumask))
>>  		return 0;
>
> So if the CPU is not the current cqm reader then the per cpu state of this
> CPU is left stale. Great improvement.
>
>> +	state->rmid = 0;
>> +	state->rmid_usecnt = 0;
>> +	wrmsr(MSR_IA32_PQR_ASSOC, 0, state->closid);
>
> What clears state->closid? And what guarantees that state->rmid is not
> updated before the CPU has really gone away?

- The rdt code takes care of clearing closid state now. Will update the comment. 
- The cqm however was never writing a zero to PQR_ASSOC.

So the update needs to be - to remove the state->closid = 0 from cqm code as the 
rdt code takes care of closid state in clear_closid() called from both offline and 
online cpu.
And also write a rmid = 0 to PQR_ASSOC.

We can integrate the two of these hot cpu calls(from cat and cqm) to write PQR 
only once.

guess I can skip all of these and send it as part of cqm changes we planned 
anyways, because this is really a cqm change.

Thanks,
Vikas