linux-kernel - Re: [PATCH v2] lib: optimize cpumask_local

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Date:   Wed, 6 Nov 2019 10:22:08 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, yuqi jin <jinyuqi@...wei.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Paul Burton <paul.burton@...s.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v2] lib: optimize cpumask_local_spread()

On Wed 06-11-19 16:02:29, Shaokun Zhang wrote:
> Hi Michal,
> 
> On 2019/11/6 15:17, Michal Hocko wrote:
> > On Tue 05-11-19 17:33:59, Andrew Morton wrote:
> >> On Tue, 5 Nov 2019 08:01:41 +0100 Michal Hocko <mhocko@...nel.org> wrote:
> >>
> >>> On Mon 04-11-19 18:27:48, Shaokun Zhang wrote:
> >>>> From: yuqi jin <jinyuqi@...wei.com>
> >>>>
> >>>> In the multi-processor and NUMA system, I/O device may have many numa
> >>>> nodes belonging to multiple cpus. When we get a local numa, it is
> >>>> better to find the node closest to the local numa node, instead
> >>>> of choosing any online cpu immediately.
> >>>>
> >>>> For the current code, it only considers the local NUMA node and it
> >>>> doesn't compute the distances between different NUMA nodes for the
> >>>> non-local NUMA nodes. Let's optimize it and find the nearest node
> >>>> through NUMA distance. The performance will be better if it return
> >>>> the nearest node than the random node.
> >>>
> >>> Numbers please
> >>
> >> The changelog had
> >>
> >> : When Parameter Server workload is tested using NIC device on Huawei
> >> : Kunpeng 920 SoC:
> >> : Without the patch, the performance is 22W QPS;
> >> : Added this patch, the performance become better and it is 26W QPS.
> > 
> > Maybe it is just me but this doesn't really tell me a lot. What is
> > Parameter Server workload? What do I do to replicate those numbers? Is
> 
> I will give it better description on it in next version. Since it returns
> the nearest node from the non-local node than the random one, no harmless
> to others, Right?

Well, I am not really familiar with consumers of this API to understand
the full consequences and that is why I keep asking. From a very
highlevel POV prefering CPUs on the same NUMA domain sounds like a
reasonable thing to do.
-- 
Michal Hocko
SUSE Labs