Date:   Thu, 22 Aug 2019 16:36:56 +0000
From:   "Derrick, Jonathan" <jonathan.derrick@...el.com>
To:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>
CC:     "hch@....de" <hch@....de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kbusch@...nel.org" <kbusch@...nel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>
Subject: Re: [PATCH V6 2/2] genirq/affinity: Spread vectors on node
 according to nr_cpu ratio

lgtm. Don't know how often we'll see these configurations but it looks
like it'll be handled gracefully
Thanks for the effort

Reviewed-by: Jon Derrick <jonathan.derrick@...el.com>

On Mon, 2019-08-19 at 20:49 +0800, Ming Lei wrote:
> Now __irq_build_affinity_masks() spreads vectors evenly per node, and
> all vectors may not be spread in case that each numa node has different
> CPU number, then the warning in irq_build_affinity_masks() can
> be triggered.
> 
> Improve current spreading algorithm by assigning vectors according to
> the ratio of node's nr_cpu to nr_remaining_cpus, meantime running the
> assignment from smaller nodes to bigger nodes to guarantee that every
> active node gets allocated at least one vector, then we can avoid
> cross-node spread in normal situation.
> 
> Meantime the reported warning can be fixed.
> 
> Another big goodness is that the spread approach becomes more fair if
> node has different CPU number.
> 
> For example, on the following machine:
> 	[root@...st-01 ~]# lscpu
> 	...
> 	CPU(s):              16
> 	On-line CPU(s) list: 0-15
> 	Thread(s) per core:  1
> 	Core(s) per socket:  8
> 	Socket(s):           2
> 	NUMA node(s):        2
> 	...
> 	NUMA node0 CPU(s):   0,1,3,5-9,11,13-15
> 	NUMA node1 CPU(s):   2,4,10,12
> 
> When driver requests to allocate 8 vectors, the following spread can
> be got:
> 	irq 31, cpu list 2,4
> 	irq 32, cpu list 10,12
> 	irq 33, cpu list 0-1
> 	irq 34, cpu list 3,5
> 	irq 35, cpu list 6-7
> 	irq 36, cpu list 8-9
> 	irq 37, cpu list 11,13
> 	irq 38, cpu list 14-15
> 
> Without this patch, kernel warning is triggered on above situation, and
> allocation result was supposed to be 4 vectors for each node.
> 
> Cc: Christoph Hellwig <hch@....de>
> Cc: Keith Busch <kbusch@...nel.org>
> Cc: linux-nvme@...ts.infradead.org,
> Cc: Jon Derrick <jonathan.derrick@...el.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Reported-by: Jon Derrick <jonathan.derrick@...el.com>
> Reviewed-by: Jon Derrick <jonathan.derrick@...el.com>
> Reviewed-by: Keith Busch <kbusch@...nel.org>
> Signed-off-by: Ming Lei <ming.lei@...hat.com>
> ---
>  kernel/irq/affinity.c | 239 +++++++++++++++++++++++++++++++++++-------
>  1 file changed, 200 insertions(+), 39 deletions(-)
> 
> diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
> index c7cca942bd8a..d905e844bf3a 100644
> --- a/kernel/irq/affinity.c
> +++ b/kernel/irq/affinity.c
> @@ -7,6 +7,7 @@
>  #include <linux/kernel.h>
>  #include <linux/slab.h>
>  #include <linux/cpu.h>
> +#include <linux/sort.h>
>  
>  static void irq_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
>  				unsigned int cpus_per_vec)
> @@ -94,6 +95,155 @@ static int get_nodes_in_cpumask(cpumask_var_t *node_to_cpumask,
>  	return nodes;
>  }
>  
> +struct node_vectors {
> +	unsigned id;
> +
> +	union {
> +		unsigned nvectors;
> +		unsigned ncpus;
> +	};
> +};
> +
> +static int ncpus_cmp_func(const void *l, const void *r)
> +{
> +	const struct node_vectors *ln = l;
> +	const struct node_vectors *rn = r;
> +
> +	return ln->ncpus - rn->ncpus;
> +}
> +
> +/*
> + * Allocate vector number for each node, so that for each node:
> + *
> + * 1) the allocated number is >= 1
> + *
> + * 2) the allocated numbver is <= active CPU number of this node
> + *
> + * The actual allocated total vectors may be less than @numvecs when
> + * active total CPU number is less than @numvecs.
> + *
> + * Active CPUs means the CPUs in '@..._mask AND @node_to_cpumask[]'
> + * for each node.
> + */
> +static void alloc_nodes_vectors(unsigned int numvecs,
> +				const cpumask_var_t *node_to_cpumask,
> +				const struct cpumask *cpu_mask,
> +				const nodemask_t nodemsk,
> +				struct cpumask *nmsk,
> +				struct node_vectors *node_vectors)
> +{
> +	unsigned n, remaining_ncpus = 0;
> +
> +	for (n = 0; n < nr_node_ids; n++) {
> +		node_vectors[n].id = n;
> +		node_vectors[n].ncpus = UINT_MAX;
> +	}
> +
> +	for_each_node_mask(n, nodemsk) {
> +		unsigned ncpus;
> +
> +		cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
> +		ncpus = cpumask_weight(nmsk);
> +
> +		if (!ncpus)
> +			continue;
> +		remaining_ncpus += ncpus;
> +		node_vectors[n].ncpus = ncpus;
> +	}
> +
> +	numvecs = min_t(unsigned, remaining_ncpus, numvecs);
> +
> +	sort(node_vectors, nr_node_ids, sizeof(node_vectors[0]),
> +	     ncpus_cmp_func, NULL);
> +
> +	/*
> +	 * Allocate vectors for each node according to the ratio of this
> +	 * node's nr_cpus to remaining un-assigned ncpus. 'numvecs' is
> +	 * bigger than number of active numa nodes. Always start the
> +	 * allocation from the node with minimized nr_cpus.
> +	 *
> +	 * This way guarantees that each active node gets allocated at
> +	 * least one vector, and the theory is simple: over-allocation
> +	 * is only done when this node is assigned by one vector, so
> +	 * other nodes will be allocated >= 1 vector, since 'numvecs' is
> +	 * bigger than number of numa nodes.
> +	 *
> +	 * One perfect invariant is that number of allocated vectors for
> +	 * each node is <= CPU count of this node:
> +	 *
> +	 * 1) suppose there are two nodes: A and B
> +	 * 	ncpu(X) is CPU count of node X
> +	 * 	vecs(X) is the vector count allocated to node X via this
> +	 * 	algorithm
> +	 *
> +	 * 	ncpu(A) <= ncpu(B)
> +	 * 	ncpu(A) + ncpu(B) = N
> +	 * 	vecs(A) + vecs(B) = V
> +	 *
> +	 * 	vecs(A) = max(1, round_down(V * ncpu(A) / N))
> +	 * 	vecs(B) = V - vecs(A)
> +	 *
> +	 * 	both N and V are integer, and 2 <= V <= N, suppose
> +	 * 	V = N - delta, and 0 <= delta <= N - 2
> +	 *
> +	 * 2) obviously vecs(A) <= ncpu(A) because:
> +	 *
> +	 * 	if vecs(A) is 1, then vecs(A) <= ncpu(A) given
> +	 * 	ncpu(A) >= 1
> +	 *
> +	 * 	otherwise,
> +	 * 		vecs(A) <= V * ncpu(A) / N <= ncpu(A), given V <= N
> +	 *
> +	 * 3) prove how vecs(B) <= ncpu(B):
> +	 *
> +	 * 	if round_down(V * ncpu(A) / N) == 0, vecs(B) won't be
> +	 * 	over-allocated, so vecs(B) <= ncpu(B),
> +	 *
> +	 * 	otherwise:
> +	 *
> +	 * 	vecs(A) =
> +	 * 		round_down(V * ncpu(A) / N) =
> +	 * 		round_down((N - delta) * ncpu(A) / N) =
> +	 * 		round_down((N * ncpu(A) - delta * ncpu(A)) / N)	 >=
> +	 * 		round_down((N * ncpu(A) - delta * N) / N)	 =
> +	 * 		cpu(A) - delta
> +	 *
> +	 * 	then:
> +	 *
> +	 * 	vecs(A) - V >= ncpu(A) - delta - V
> +	 * 	=>
> +	 * 	V - vecs(A) <= V + delta - ncpu(A)
> +	 * 	=>
> +	 * 	vecs(B) <= N - ncpu(A)
> +	 * 	=>
> +	 * 	vecs(B) <= cpu(B)
> +	 *
> +	 * For nodes >= 3, it can be thought as one node and another big
> +	 * node given that is exactly what this algorithm is implemented,
> +	 * and we always re-calculate 'remaining_ncpus' & 'numvecs', and
> +	 * finally for each node X: vecs(X) <= ncpu(X).
> +	 *
> +	 */
> +	for (n = 0; n < nr_node_ids; n++) {
> +		unsigned nvectors, ncpus;
> +
> +		if (node_vectors[n].ncpus == UINT_MAX)
> +			continue;
> +
> +		WARN_ON_ONCE(numvecs == 0);
> +
> +		ncpus = node_vectors[n].ncpus;
> +		nvectors = max_t(unsigned, 1,
> +				 numvecs * ncpus / remaining_ncpus);
> +		WARN_ON_ONCE(nvectors > ncpus);
> +
> +		node_vectors[n].nvectors = nvectors;
> +
> +		remaining_ncpus -= ncpus;
> +		numvecs -= nvectors;
> +	}
> +}
> +
>  static int __irq_build_affinity_masks(unsigned int startvec,
>  				      unsigned int numvecs,
>  				      unsigned int firstvec,
> @@ -102,10 +252,11 @@ static int __irq_build_affinity_masks(unsigned int startvec,
>  				      struct cpumask *nmsk,
>  				      struct irq_affinity_desc *masks)
>  {
> -	unsigned int n, nodes, cpus_per_vec, extra_vecs, done = 0;
> +	unsigned int i, n, nodes, cpus_per_vec, extra_vecs, done = 0;
>  	unsigned int last_affv = firstvec + numvecs;
>  	unsigned int curvec = startvec;
>  	nodemask_t nodemsk = NODE_MASK_NONE;
> +	struct node_vectors *node_vectors;
>  
>  	if (!cpumask_weight(cpu_mask))
>  		return 0;
> @@ -126,53 +277,57 @@ static int __irq_build_affinity_masks(unsigned int startvec,
>  		return numvecs;
>  	}
>  
> -	for_each_node_mask(n, nodemsk) {
> -		unsigned int ncpus, v, vecs_to_assign, vecs_per_node;
> +	node_vectors = kcalloc(nr_node_ids,
> +			       sizeof(struct node_vectors),
> +			       GFP_KERNEL);
> +	if (!node_vectors)
> +		return -ENOMEM;
> +
> +	/* allocate vector number for each node */
> +	alloc_nodes_vectors(numvecs, node_to_cpumask, cpu_mask,
> +			    nodemsk, nmsk, node_vectors);
> +
> +	for (i = 0; i < nr_node_ids; i++) {
> +		unsigned int ncpus, v;
> +		struct node_vectors *nv = &node_vectors[i];
> +
> +		if (nv->nvectors == UINT_MAX)
> +			continue;
>  
>  		/* Get the cpus on this node which are in the mask */
> -		cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
> +		cpumask_and(nmsk, cpu_mask, node_to_cpumask[nv->id]);
>  		ncpus = cpumask_weight(nmsk);
>  		if (!ncpus)
>  			continue;
>  
> -		/*
> -		 * Calculate the number of cpus per vector
> -		 *
> -		 * Spread the vectors evenly per node. If the requested
> -		 * vector number has been reached, simply allocate one
> -		 * vector for each remaining node so that all nodes can
> -		 * be covered
> -		 */
> -		if (numvecs > done)
> -			vecs_per_node = max_t(unsigned,
> -					(numvecs - done) / nodes, 1);
> -		else
> -			vecs_per_node = 1;
> -
> -		vecs_to_assign = min(vecs_per_node, ncpus);
> +		WARN_ON_ONCE(nv->nvectors > ncpus);
>  
>  		/* Account for rounding errors */
> -		extra_vecs = ncpus - vecs_to_assign * (ncpus / vecs_to_assign);
> +		extra_vecs = ncpus - nv->nvectors * (ncpus / nv->nvectors);
>  
> -		for (v = 0; curvec < last_affv && v < vecs_to_assign;
> -		     curvec++, v++) {
> -			cpus_per_vec = ncpus / vecs_to_assign;
> +		/* Spread allocated vectors on CPUs of the current node */
> +		for (v = 0; v < nv->nvectors; v++, curvec++) {
> +			cpus_per_vec = ncpus / nv->nvectors;
>  
>  			/* Account for extra vectors to compensate rounding errors */
>  			if (extra_vecs) {
>  				cpus_per_vec++;
>  				--extra_vecs;
>  			}
> +
> +			/*
> +			 * wrapping has to be considered given 'startvec'
> +			 * may start anywhere
> +			 */
> +			if (curvec >= last_affv)
> +				curvec = firstvec;
>  			irq_spread_init_one(&masks[curvec].mask, nmsk,
>  						cpus_per_vec);
>  		}
> -
> -		done += v;
> -		if (curvec >= last_affv)
> -			curvec = firstvec;
> -		--nodes;
> +		done += nv->nvectors;
>  	}
> -	return done < numvecs ? done : numvecs;
> +	kfree(node_vectors);
> +	return done;
>  }
>  
>  /*
> @@ -184,7 +339,7 @@ static int irq_build_affinity_masks(unsigned int startvec, unsigned int numvecs,
>  				    unsigned int firstvec,
>  				    struct irq_affinity_desc *masks)
>  {
> -	unsigned int curvec = startvec, nr_present, nr_others;
> +	unsigned int curvec = startvec, nr_present = 0, nr_others = 0;
>  	cpumask_var_t *node_to_cpumask;
>  	cpumask_var_t nmsk, npresmsk;
>  	int ret = -ENOMEM;
> @@ -199,15 +354,17 @@ static int irq_build_affinity_masks(unsigned int startvec, unsigned int numvecs,
>  	if (!node_to_cpumask)
>  		goto fail_npresmsk;
>  
> -	ret = 0;
>  	/* Stabilize the cpumasks */
>  	get_online_cpus();
>  	build_node_to_cpumask(node_to_cpumask);
>  
>  	/* Spread on present CPUs starting from affd->pre_vectors */
> -	nr_present = __irq_build_affinity_masks(curvec, numvecs,
> -						firstvec, node_to_cpumask,
> -						cpu_present_mask, nmsk, masks);
> +	ret = __irq_build_affinity_masks(curvec, numvecs, firstvec,
> +					 node_to_cpumask, cpu_present_mask,
> +					 nmsk, masks);
> +	if (ret < 0)
> +		goto fail_build_affinity;
> +	nr_present = ret;
>  
>  	/*
>  	 * Spread on non present CPUs starting from the next vector to be
> @@ -220,12 +377,16 @@ static int irq_build_affinity_masks(unsigned int startvec, unsigned int numvecs,
>  	else
>  		curvec = firstvec + nr_present;
>  	cpumask_andnot(npresmsk, cpu_possible_mask, cpu_present_mask);
> -	nr_others = __irq_build_affinity_masks(curvec, numvecs,
> -					       firstvec, node_to_cpumask,
> -					       npresmsk, nmsk, masks);
> +	ret = __irq_build_affinity_masks(curvec, numvecs, firstvec,
> +					 node_to_cpumask, npresmsk, nmsk,
> +					 masks);
> +	if (ret >= 0)
> +		nr_others = ret;
> +
> + fail_build_affinity:
>  	put_online_cpus();
>  
> -	if (nr_present < numvecs)
> +	if (ret >= 0)
>  		WARN_ON(nr_present + nr_others < numvecs);
>  
>  	free_node_to_cpumask(node_to_cpumask);
> @@ -235,7 +396,7 @@ static int irq_build_affinity_masks(unsigned int startvec, unsigned int numvecs,
>  
>   fail_nmsk:
>  	free_cpumask_var(nmsk);
> -	return ret;
> +	return ret < 0 ? ret : 0;
>  }
>  
>  static void default_calc_sets(struct irq_affinity *affd, unsigned int affvecs)

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