Date:   Tue, 12 Nov 2019 12:56:30 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>
Cc:     linux-kernel@...r.kernel.org, yuqi jin <jinyuqi@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Paul Burton <paul.burton@...s.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Anshuman Khandual <anshuman.khandual@....com>,
        netdev@...r.kernel.org
Subject: Re: [PATCH v3] lib: optimize cpumask_local_spread()

On Mon 11-11-19 10:02:37, Shaokun Zhang wrote:
> Hi Michal,
> 
> On 2019/11/8 18:31, Michal Hocko wrote:
> > 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)
> 
> Oh, I forgot to involve the net guys, sorry.
> 
> > 
> > On Thu 07-11-19 09:44:08, Shaokun Zhang wrote:
> >> From: yuqi jin <jinyuqi@...wei.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).
> > 
> 
> available: 4 nodes (0-3)
> node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
> node 0 size: 63379 MB
> node 0 free: 61899 MB
> node 1 cpus: 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
> node 1 size: 64509 MB
> node 1 free: 63942 MB
> node 2 cpus: 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71
> node 2 size: 64509 MB
> node 2 free: 63056 MB
> node 3 cpus: 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
> node 3 size: 63997 MB
> node 3 free: 63420 MB
> node distances:
> node   0   1   2   3
>   0:  10  16  32  33
>   1:  16  10  25  32
>   2:  32  25  10  16
>   3:  33  32  16  10
> 
> >> 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?
> > 
> 
> Sorry, the PS which we test is not open, but I think redis is the same as PS
> on the macro level. When there are both 24 redis servers on node2 and node3.
> if the 24-47 irqs and xps of NIC are not bound to node3, the redis servers
> on node3 will not performance good.

Are there any other benchmarks showing improvements?

> >> 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?
> > 
> 
> Before this patch
> Euler:/sys/bus/pci/devices/0000:7d:00.2 # cat numa_node
> 2
> Euler:~ # cat /proc/irq/345/smp_affinity    #IRQ0
> 00000000,00010000,00000000

This representation is awkward to parse. Could you add smp_affinity_list
please? It would save quite some head scratching.
-- 
Michal Hocko
SUSE Labs

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