Re: [PATCH 1/2] KVM: PPC: Book3S HV: Simplify dynamic micro-threading code

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On Tue, Jun 27, 2017 at 04:07:56PM +1000, Paul Mackerras wrote:
> Since commit b009031f74da ("KVM: PPC: Book3S HV: Take out virtual
> core piggybacking code", 2016-09-15), we only have at most one
> vcore per subcore.  Previously, the fact that there might be more
> than one vcore per subcore meant that we had the notion of a
> "master vcore", which was the vcore that controlled thread 0 of
> the subcore.  We also needed a list per subcore in the core_info
> struct to record which vcores belonged to each subcore.  Now that
> there can only be one vcore in the subcore, we can replace the
> list with a simple pointer and get rid of the notion of the
> master vcore (and in fact treat every vcore as a master vcore).
> 
> We can also get rid of the subcore_vm[] field in the core_info
> struct since it is never read.
> 
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>

Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>

> ---
>  arch/powerpc/include/asm/kvm_book3s.h     |  1 -
>  arch/powerpc/include/asm/kvm_book3s_asm.h |  2 +-
>  arch/powerpc/kvm/book3s_hv.c              | 88 +++++++++++++------------------
>  arch/powerpc/kvm/book3s_hv_builtin.c      |  2 +-
>  4 files changed, 39 insertions(+), 54 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
> index 2bf35017ffc0..b8d5b8e35244 100644
> --- a/arch/powerpc/include/asm/kvm_book3s.h
> +++ b/arch/powerpc/include/asm/kvm_book3s.h
> @@ -86,7 +86,6 @@ struct kvmppc_vcore {
>  	u16 last_cpu;
>  	u8 vcore_state;
>  	u8 in_guest;
> -	struct kvmppc_vcore *master_vcore;
>  	struct kvm_vcpu *runnable_threads[MAX_SMT_THREADS];
>  	struct list_head preempt_list;
>  	spinlock_t lock;
> diff --git a/arch/powerpc/include/asm/kvm_book3s_asm.h b/arch/powerpc/include/asm/kvm_book3s_asm.h
> index b148496ffe36..7cea76f11c26 100644
> --- a/arch/powerpc/include/asm/kvm_book3s_asm.h
> +++ b/arch/powerpc/include/asm/kvm_book3s_asm.h
> @@ -81,7 +81,7 @@ struct kvm_split_mode {
>  	u8		subcore_size;
>  	u8		do_nap;
>  	u8		napped[MAX_SMT_THREADS];
> -	struct kvmppc_vcore *master_vcs[MAX_SUBCORES];
> +	struct kvmppc_vcore *vc[MAX_SUBCORES];
>  };
>  
>  /*
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index c4ada89be658..03d6c7f9b547 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -2171,7 +2171,6 @@ static void kvmppc_start_thread(struct kvm_vcpu *vcpu, struct kvmppc_vcore *vc)
>  {
>  	int cpu;
>  	struct paca_struct *tpaca;
> -	struct kvmppc_vcore *mvc = vc->master_vcore;
>  	struct kvm *kvm = vc->kvm;
>  
>  	cpu = vc->pcpu;
> @@ -2181,7 +2180,7 @@ static void kvmppc_start_thread(struct kvm_vcpu *vcpu, struct kvmppc_vcore *vc)
>  			vcpu->arch.timer_running = 0;
>  		}
>  		cpu += vcpu->arch.ptid;
> -		vcpu->cpu = mvc->pcpu;
> +		vcpu->cpu = vc->pcpu;
>  		vcpu->arch.thread_cpu = cpu;
>  
>  		/*
> @@ -2207,10 +2206,10 @@ static void kvmppc_start_thread(struct kvm_vcpu *vcpu, struct kvmppc_vcore *vc)
>  	}
>  	tpaca = &paca[cpu];
>  	tpaca->kvm_hstate.kvm_vcpu = vcpu;
> -	tpaca->kvm_hstate.ptid = cpu - mvc->pcpu;
> +	tpaca->kvm_hstate.ptid = cpu - vc->pcpu;
>  	/* Order stores to hstate.kvm_vcpu etc. before store to kvm_vcore */
>  	smp_wmb();
> -	tpaca->kvm_hstate.kvm_vcore = mvc;
> +	tpaca->kvm_hstate.kvm_vcore = vc;
>  	if (cpu != smp_processor_id())
>  		kvmppc_ipi_thread(cpu);
>  }
> @@ -2339,8 +2338,7 @@ struct core_info {
>  	int		max_subcore_threads;
>  	int		total_threads;
>  	int		subcore_threads[MAX_SUBCORES];
> -	struct kvm	*subcore_vm[MAX_SUBCORES];
> -	struct list_head vcs[MAX_SUBCORES];
> +	struct kvmppc_vcore *vc[MAX_SUBCORES];
>  };
>  
>  /*
> @@ -2351,17 +2349,12 @@ static int subcore_thread_map[MAX_SUBCORES] = { 0, 4, 2, 6 };
>  
>  static void init_core_info(struct core_info *cip, struct kvmppc_vcore *vc)
>  {
> -	int sub;
> -
>  	memset(cip, 0, sizeof(*cip));
>  	cip->n_subcores = 1;
>  	cip->max_subcore_threads = vc->num_threads;
>  	cip->total_threads = vc->num_threads;
>  	cip->subcore_threads[0] = vc->num_threads;
> -	cip->subcore_vm[0] = vc->kvm;
> -	for (sub = 0; sub < MAX_SUBCORES; ++sub)
> -		INIT_LIST_HEAD(&cip->vcs[sub]);
> -	list_add_tail(&vc->preempt_list, &cip->vcs[0]);
> +	cip->vc[0] = vc;
>  }
>  
>  static bool subcore_config_ok(int n_subcores, int n_threads)
> @@ -2381,9 +2374,8 @@ static bool subcore_config_ok(int n_subcores, int n_threads)
>  	return n_subcores * roundup_pow_of_two(n_threads) <= MAX_SMT_THREADS;
>  }
>  
> -static void init_master_vcore(struct kvmppc_vcore *vc)
> +static void init_vcore_to_run(struct kvmppc_vcore *vc)
>  {
> -	vc->master_vcore = vc;
>  	vc->entry_exit_map = 0;
>  	vc->in_guest = 0;
>  	vc->napping_threads = 0;
> @@ -2408,9 +2400,9 @@ static bool can_dynamic_split(struct kvmppc_vcore *vc, struct core_info *cip)
>  	++cip->n_subcores;
>  	cip->total_threads += vc->num_threads;
>  	cip->subcore_threads[sub] = vc->num_threads;
> -	cip->subcore_vm[sub] = vc->kvm;
> -	init_master_vcore(vc);
> -	list_move_tail(&vc->preempt_list, &cip->vcs[sub]);
> +	cip->vc[sub] = vc;
> +	init_vcore_to_run(vc);
> +	list_del_init(&vc->preempt_list);
>  
>  	return true;
>  }
> @@ -2515,7 +2507,6 @@ static void post_guest_process(struct kvmppc_vcore *vc, bool is_master)
>  			wake_up(&vcpu->arch.cpu_run);
>  		}
>  	}
> -	list_del_init(&vc->preempt_list);
>  	if (!is_master) {
>  		if (still_running > 0) {
>  			kvmppc_vcore_preempt(vc);
> @@ -2587,7 +2578,7 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  	int i;
>  	int srcu_idx;
>  	struct core_info core_info;
> -	struct kvmppc_vcore *pvc, *vcnext;
> +	struct kvmppc_vcore *pvc;
>  	struct kvm_split_mode split_info, *sip;
>  	int split, subcore_size, active;
>  	int sub;
> @@ -2610,7 +2601,7 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  	/*
>  	 * Initialize *vc.
>  	 */
> -	init_master_vcore(vc);
> +	init_vcore_to_run(vc);
>  	vc->preempt_tb = TB_NIL;
>  
>  	/*
> @@ -2670,9 +2661,7 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  		split_info.ldbar = mfspr(SPRN_LDBAR);
>  		split_info.subcore_size = subcore_size;
>  		for (sub = 0; sub < core_info.n_subcores; ++sub)
> -			split_info.master_vcs[sub] =
> -				list_first_entry(&core_info.vcs[sub],
> -					struct kvmppc_vcore, preempt_list);
> +			split_info.vc[sub] = core_info.vc[sub];
>  		/* order writes to split_info before kvm_split_mode pointer */
>  		smp_wmb();
>  	}
> @@ -2704,24 +2693,23 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  		thr = subcore_thread_map[sub];
>  		thr0_done = false;
>  		active |= 1 << thr;
> -		list_for_each_entry(pvc, &core_info.vcs[sub], preempt_list) {
> -			pvc->pcpu = pcpu + thr;
> -			for_each_runnable_thread(i, vcpu, pvc) {
> -				kvmppc_start_thread(vcpu, pvc);
> -				kvmppc_create_dtl_entry(vcpu, pvc);
> -				trace_kvm_guest_enter(vcpu);
> -				if (!vcpu->arch.ptid)
> -					thr0_done = true;
> -				active |= 1 << (thr + vcpu->arch.ptid);
> -			}
> -			/*
> -			 * We need to start the first thread of each subcore
> -			 * even if it doesn't have a vcpu.
> -			 */
> -			if (pvc->master_vcore == pvc && !thr0_done)
> -				kvmppc_start_thread(NULL, pvc);
> -			thr += pvc->num_threads;
> +		pvc = core_info.vc[sub];
> +		pvc->pcpu = pcpu + thr;
> +		for_each_runnable_thread(i, vcpu, pvc) {
> +			kvmppc_start_thread(vcpu, pvc);
> +			kvmppc_create_dtl_entry(vcpu, pvc);
> +			trace_kvm_guest_enter(vcpu);
> +			if (!vcpu->arch.ptid)
> +				thr0_done = true;
> +			active |= 1 << (thr + vcpu->arch.ptid);
>  		}
> +		/*
> +		 * We need to start the first thread of each subcore
> +		 * even if it doesn't have a vcpu.
> +		 */
> +		if (!thr0_done)
> +			kvmppc_start_thread(NULL, pvc);
> +		thr += pvc->num_threads;
>  	}
>  
>  	/*
> @@ -2748,8 +2736,7 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  	trace_kvmppc_run_core(vc, 0);
>  
>  	for (sub = 0; sub < core_info.n_subcores; ++sub)
> -		list_for_each_entry(pvc, &core_info.vcs[sub], preempt_list)
> -			spin_unlock(&pvc->lock);
> +		spin_unlock(&core_info.vc[sub]->lock);
>  
>  	guest_enter();
>  
> @@ -2802,10 +2789,10 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  	smp_mb();
>  	guest_exit();
>  
> -	for (sub = 0; sub < core_info.n_subcores; ++sub)
> -		list_for_each_entry_safe(pvc, vcnext, &core_info.vcs[sub],
> -					 preempt_list)
> -			post_guest_process(pvc, pvc == vc);
> +	for (sub = 0; sub < core_info.n_subcores; ++sub) {
> +		pvc = core_info.vc[sub];
> +		post_guest_process(pvc, pvc == vc);
> +	}
>  
>  	spin_lock(&vc->lock);
>  	preempt_enable();
> @@ -3026,15 +3013,14 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
>  	 */
>  	if (!signal_pending(current)) {
>  		if (vc->vcore_state == VCORE_PIGGYBACK) {
> -			struct kvmppc_vcore *mvc = vc->master_vcore;
> -			if (spin_trylock(&mvc->lock)) {
> -				if (mvc->vcore_state == VCORE_RUNNING &&
> -				    !VCORE_IS_EXITING(mvc)) {
> +			if (spin_trylock(&vc->lock)) {
> +				if (vc->vcore_state == VCORE_RUNNING &&
> +				    !VCORE_IS_EXITING(vc)) {
>  					kvmppc_create_dtl_entry(vcpu, vc);
>  					kvmppc_start_thread(vcpu, vc);
>  					trace_kvm_guest_enter(vcpu);
>  				}
> -				spin_unlock(&mvc->lock);
> +				spin_unlock(&vc->lock);
>  			}
>  		} else if (vc->vcore_state == VCORE_RUNNING &&
>  			   !VCORE_IS_EXITING(vc)) {
> diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c
> index ee4c2558c305..90644db9d38e 100644
> --- a/arch/powerpc/kvm/book3s_hv_builtin.c
> +++ b/arch/powerpc/kvm/book3s_hv_builtin.c
> @@ -307,7 +307,7 @@ void kvmhv_commence_exit(int trap)
>  		return;
>  
>  	for (i = 0; i < MAX_SUBCORES; ++i) {
> -		vc = sip->master_vcs[i];
> +		vc = sip->vc[i];
>  		if (!vc)
>  			break;
>  		do {

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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