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Date:   Thu, 21 Dec 2017 18:31:19 +0800
From:   kemi <>
To:     Michal Hocko <>
Cc:     Greg Kroah-Hartman <>,
        Andrew Morton <>,
        Vlastimil Babka <>,
        Mel Gorman <>,
        Johannes Weiner <>,
        Christopher Lameter <>,
        Andrey Ryabinin <>,
        Nikolay Borisov <>,
        Pavel Tatashin <>,
        David Rientjes <>,
        Sebastian Andrzej Siewior <>,
        Dave <>,
        Andi Kleen <>,
        Tim Chen <>,
        Jesper Dangaard Brouer <>,
        Ying Huang <>,
        Aaron Lu <>, Aubrey Li <>,
        Linux MM <>,
        Linux Kernel <>
Subject: Re: [PATCH v2 3/5] mm: enlarge NUMA counters threshold size

On 2017年12月21日 16:59, Michal Hocko wrote:
> On Thu 21-12-17 16:23:23, kemi wrote:
>> On 2017年12月21日 16:17, Michal Hocko wrote:
> [...]
>>> Can you see any difference with a more generic workload?
>> I didn't see obvious improvement for will-it-scale.page_fault1
>> Two reasons for that:
>> 1) too long code path
>> 2) server zone lock and lru lock contention (access to buddy system frequently) 
> OK. So does the patch helps for anything other than a microbenchmark?
>>>> Some thinking about that:
>>>> a) the overhead due to cache bouncing caused by NUMA counter update in fast path 
>>>> severely increase with more and more CPUs cores
>>> What is an effect on a smaller system with fewer CPUs?
>> Several CPU cycles can be saved using single thread for that.
>>>> b) AFAIK, the typical usage scenario (similar at least)for which this optimization can 
>>>> benefit is 10/40G NIC used in high-speed data center network of cloud service providers.
>>> I would expect those would disable the numa accounting altogether.
>> Yes, but it is still worthy to do some optimization, isn't?
> Ohh, I am not opposing optimizations but you should make sure that they
> are worth the additional code and special casing. As I've said I am not
> convinced special casing numa counters is good. You can play with the
> threshold scaling for larger CPU count but let's make sure that the
> benefit is really measurable for normal workloads. Special ones will
> disable the numa accounting anyway.

I understood. Could you give me some suggestion for those normal workloads, Thanks.
I will have a try and post the data ASAP. 

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