Messages in this thread | | | Date | Fri, 8 Nov 2019 11:31:02 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH v3] lib: optimize cpumask_local_spread() |
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This changelog looks better, thanks! I still have some questions though. Btw. cpumask_local_spread is used by the networking code but I do not see net guys involved (Cc netdev)
On Thu 07-11-19 09:44:08, Shaokun Zhang wrote: > From: yuqi jin <jinyuqi@huawei.com> > > In the multi-processors and NUMA system, I/O driver will find cpu cores > that which shall be bound IRQ. When cpu cores in the local numa have > been used, it is better to find the node closest to the local numa node, > instead of choosing any online cpu immediately. > > On Huawei Kunpeng 920 server, there are 4 NUMA node(0 -3) in the 2-cpu > system(0 - 1).
Please send a topology of this server (numactl -H).
> We perform PS (parameter server) business test, the > behavior of the service is that the client initiates a request through > the network card, the server responds to the request after calculation.
Is the benchmark any ublicly available?
> When two PS processes run on node2 and node3 separately and the > network card is located on 'node2' which is in cpu1, the performance > of node2 (26W QPS) and node3 (22W QPS) was different. > It is better that the NIC queues are bound to the cpu1 cores in turn, > then XPS will also be properly initialized, while cpumask_local_spread > only considers the local node. When the number of NIC queues exceeds > the number of cores in the local node, it returns to the online core > directly. So when PS runs on node3 sending a calculated request, > the performance is not as good as the node2. It is considered that > the NIC and other I/O devices shall initialize the interrupt binding, > if the cores of the local node are used up, it is reasonable to return > the node closest to it.
Can you post cpu affinities before and after this patch?
> Let's optimize it and find the nearest node through NUMA distance for the > non-local NUMA nodes. The performance will be better if it return the > nearest node than the random node. > > After this patch, the performance of the node3 is the same as node2 > that is 26W QPS when the network card is still in 'node2'. Since it will > return the closest non-local NUMA code rather than random node, it is no > harm to others at least.
It would be also nice to explain why the current implementation hasn't taken the path your have chosen. Was it a simplicity or is there a more fundamental reason? Is there any risk that existing users would regress? Preferring cpus from the local socket which is what you aim for sounds like a logical thing to do so I am wondering why this hasn't been considered.
> Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Mike Rapoport <rppt@linux.ibm.com> > Cc: Paul Burton <paul.burton@mips.com> > Cc: Michal Hocko <mhocko@suse.com> > Cc: Michael Ellerman <mpe@ellerman.id.au> > Cc: Anshuman Khandual <anshuman.khandual@arm.com> > Signed-off-by: yuqi jin <jinyuqi@huawei.com> > Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com> > --- > ChangeLog from v2: > 1. Change the variables as static and use spinlock to protect; > 2. Give more explantation on test and performance; > lib/cpumask.c | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 90 insertions(+), 12 deletions(-) > > diff --git a/lib/cpumask.c b/lib/cpumask.c > index 0cb672eb107c..b98a2256bc5a 100644 > --- a/lib/cpumask.c > +++ b/lib/cpumask.c > @@ -6,6 +6,7 @@ > #include <linux/export.h> > #include <linux/memblock.h> > #include <linux/numa.h> > +#include <linux/spinlock.h> > > /** > * cpumask_next - get the next cpu in a cpumask > @@ -192,18 +193,39 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask) > } > #endif > > -/** > - * cpumask_local_spread - select the i'th cpu with local numa cpu's first > - * @i: index number > - * @node: local numa_node > - * > - * This function selects an online CPU according to a numa aware policy; > - * local cpus are returned first, followed by non-local ones, then it > - * wraps around. > - * > - * It's not very efficient, but useful for setup. > - */ > -unsigned int cpumask_local_spread(unsigned int i, int node) > +static void calc_node_distance(int *node_dist, int node) > +{ > + int i; > + > + for (i = 0; i < nr_node_ids; i++) > + node_dist[i] = node_distance(node, i); > +} > + > +static int find_nearest_node(int *node_dist, bool *used) > +{ > + int i, min_dist = node_dist[0], node_id = -1; > + > + /* Choose the first unused node to compare */ > + for (i = 0; i < nr_node_ids; i++) { > + if (used[i] == 0) { > + min_dist = node_dist[i]; > + node_id = i; > + break; > + } > + } > + > + /* Compare and return the nearest node */ > + for (i = 0; i < nr_node_ids; i++) { > + if (node_dist[i] < min_dist && used[i] == 0) { > + min_dist = node_dist[i]; > + node_id = i; > + } > + } > + > + return node_id; > +} > + > +static unsigned int __cpumask_local_spread(unsigned int i, int node) > { > int cpu; > > @@ -231,4 +253,60 @@ unsigned int cpumask_local_spread(unsigned int i, int node) > } > BUG(); > } > + > +static DEFINE_SPINLOCK(spread_lock); > +/** > + * cpumask_local_spread - select the i'th cpu with local numa cpu's first > + * @i: index number > + * @node: local numa_node > + * > + * This function selects an online CPU according to a numa aware policy; > + * local cpus are returned first, followed by the nearest non-local ones, > + * then it wraps around. > + * > + * It's not very efficient, but useful for setup. > + */ > +unsigned int cpumask_local_spread(unsigned int i, int node) > +{ > + static int node_dist[MAX_NUMNODES]; > + static bool used[MAX_NUMNODES]; > + unsigned long flags; > + int cpu, j, id; > + > + /* Wrap: we always want a cpu. */ > + i %= num_online_cpus(); > + > + if (node == NUMA_NO_NODE) { > + for_each_cpu(cpu, cpu_online_mask) > + if (i-- == 0) > + return cpu; > + } else { > + if (nr_node_ids > MAX_NUMNODES) > + return __cpumask_local_spread(i, node); > + > + spin_lock_irqsave(&spread_lock, flags); > + memset(used, 0, nr_node_ids * sizeof(bool)); > + calc_node_distance(node_dist, node); > + for (j = 0; j < nr_node_ids; j++) { > + id = find_nearest_node(node_dist, used); > + if (id < 0) > + break; > + > + for_each_cpu_and(cpu, cpumask_of_node(id), > + cpu_online_mask) > + if (i-- == 0) { > + spin_unlock_irqrestore(&spread_lock, > + flags); > + return cpu; > + } > + used[id] = 1; > + } > + spin_unlock_irqrestore(&spread_lock, flags); > + > + for_each_cpu(cpu, cpu_online_mask) > + if (i-- == 0) > + return cpu; > + } > + BUG(); > +} > EXPORT_SYMBOL(cpumask_local_spread); > -- > 2.7.4
-- Michal Hocko SUSE Labs
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