linux-kernel - Re: [PATCH 17/21] x86/intel_rdt/cqm: Add sched

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Date:   Thu, 6 Jul 2017 16:35:17 -0700 (PDT)
From:   Shivappa Vikas <vikas.shivappa@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
cc:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, hpa@...or.com, peterz@...radead.org,
        ravi.v.shankar@...el.com, vikas.shivappa@...el.com,
        tony.luck@...el.com, fenghua.yu@...el.com, andi.kleen@...el.com
Subject: Re: [PATCH 17/21] x86/intel_rdt/cqm: Add sched_in support



On Sun, 2 Jul 2017, Thomas Gleixner wrote:

> On Mon, 26 Jun 2017, Vikas Shivappa wrote:
>>  DECLARE_PER_CPU(struct intel_pqr_state, pqr_state);
>>  DECLARE_PER_CPU_READ_MOSTLY(int, cpu_closid);
>> +DECLARE_PER_CPU_READ_MOSTLY(int, cpu_rmid);
>>  DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
>> +DECLARE_STATIC_KEY_FALSE(rdt_mon_enable_key);
>> +DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
>
> Please make this a two stage change. Add rdt_enable_key first and then the
> monitoring stuff. Ideally you introduce rdt_enable_key here and in the
> control code in one go.
>
>> +static void __intel_rdt_sched_in(void)
>>  {
>> -	if (static_branch_likely(&rdt_alloc_enable_key)) {
>> -		struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
>> -		int closid;
>> +	struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
>> +	u32 closid = 0;
>> +	u32 rmid = 0;
>>
>> +	if (static_branch_likely(&rdt_alloc_enable_key)) {
>>  		/*
>>  		 * If this task has a closid assigned, use it.
>>  		 * Else use the closid assigned to this cpu.
>> @@ -55,14 +59,31 @@ static inline void intel_rdt_sched_in(void)
>>  		closid = current->closid;
>>  		if (closid == 0)
>>  			closid = this_cpu_read(cpu_closid);
>> +	}
>> +
>> +	if (static_branch_likely(&rdt_mon_enable_key)) {
>> +		/*
>> +		 * If this task has a rmid assigned, use it.
>> +		 * Else use the rmid assigned to this cpu.
>> +		 */
>> +		rmid = current->rmid;
>> +		if (rmid == 0)
>> +			rmid = this_cpu_read(cpu_rmid);
>> +	}
>>
>> -		if (closid != state->closid) {
>> -			state->closid = closid;
>> -			wrmsr(IA32_PQR_ASSOC, state->rmid, closid);
>> -		}
>> +	if (closid != state->closid || rmid != state->rmid) {
>> +		state->closid = closid;
>> +		state->rmid = rmid;
>> +		wrmsr(IA32_PQR_ASSOC, rmid, closid);
>
> This can be written smarter.
>
> 	struct intel_pqr_state newstate = this_cpu_read(rdt_cpu_default);
> 	struct intel_pqr_state *curstate = this_cpu_ptr(&pqr_state);
>
> 	if (static_branch_likely(&rdt_alloc_enable_key)) {
> 		if (current->closid)
> 			newstate.closid = current->closid;
> 	}
>
> 	if (static_branch_likely(&rdt_mon_enable_key)) {
> 		if (current->rmid)
> 			newstate.rmid = current->rmid;
> 	}
>
> 	if (newstate != *curstate) {
> 		*curstate = newstate;
> 		wrmsr(IA32_PQR_ASSOC, newstate.rmid, newstate.closid);
> 	}
>
> The unconditional read of rdt_cpu_default is the right thing to do because
> the default behaviour is exactly this.

Ok makes sense. Will fix.

Thanks,
Vikas
>
> Thanks,
>
> 	tglx
>
>
>
>