netdev - Re: Page allocator bottleneck

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Date:   Sun, 17 Sep 2017 18:43:09 +0300
From:   Tariq Toukan <tariqt@...lanox.com>
To:     Andi Kleen <ak@...ux.intel.com>, Tariq Toukan <tariqt@...lanox.com>
Cc:     David Miller <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, linux-mm <linux-mm@...ck.org>
Subject: Re: Page allocator bottleneck



On 14/09/2017 11:19 PM, Andi Kleen wrote:
> Tariq Toukan <tariqt@...lanox.com> writes:
>>
>> Congestion in this case is very clear.
>> When monitored in perf top:
>> 85.58% [kernel] [k] queued_spin_lock_slowpath
> 
> Please look at the callers. Spinlock profiles without callers
> are usually useless because it's just blaming the messenger.
> 
> Most likely the PCP lists are too small for your extreme allocation
> rate, so it goes back too often to the shared pool.
> 
> You can play with the vm.percpu_pagelist_fraction setting.

Thanks Andi.
That was my initial guess, but I wasn't familiar with these tunes in VM 
to verify that.
Indeed, bottleneck is released when increasing the PCP size, and BW 
becomes significantly better.

> 
> -Andi
>