netdev - Re: Page allocator bottleneck

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Date:   Fri, 27 Apr 2018 16:45:58 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     Tariq Toukan <tariqt@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        David Miller <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: Page allocator bottleneck

On Mon, Apr 23, 2018 at 09:10:33PM +0800, Aaron Lu wrote:
> On Mon, Apr 23, 2018 at 11:54:57AM +0300, Tariq Toukan wrote:
> > Hi,
> > 
> > I ran my tests with your patches.
> > Initial BW numbers are significantly higher than I documented back then in
> > this mail-thread.
> > For example, in driver #2 (see original mail thread), with 6 rings, I now
> > get 92Gbps (slightly less than linerate) in comparison to 64Gbps back then.
> > 
> > However, there were many kernel changes since then, I need to isolate your
> > changes. I am not sure I can finish this today, but I will surely get to it
> > next week after I'm back from vacation.
> > 
> > Still, when I increase the scale (more rings, i.e. more cpus), I see that
> > queued_spin_lock_slowpath gets to 60%+ cpu. Still high, but lower than it
> > used to be.
> 
> I wonder if it is on allocation path or free path?

Just FYI, I have pushed two more commits on top of the branch.
They should improve free path zone lock contention for MIGRATE_UNMOVABLE
pages(most kernel code alloc such pages), you may consider apply them if
free path contention is a problem.