linux-kernel - Re: [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v6

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Date:   Fri, 8 May 2020 13:05:36 +0200
From:   Jirka Hladky <jhladky@...hat.com>
To:     linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/13] Reconcile NUMA balancing decisions with the load
 balancer v6

Hi Mel,

thanks for hints! We will try it.

@Phil - could you please prepare a kernel build for me to test?

Thank you!
Jirka

On Fri, May 8, 2020 at 11:22 AM Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> On Thu, May 07, 2020 at 06:29:44PM +0200, Jirka Hladky wrote:
> > Hi Mel,
> >
> > we are not targeting just OMP applications. We see the performance
> > degradation also for other workloads, like SPECjbb2005 and
> > SPECjvm2008. Even worse, it also affects a higher number of threads.
> > For example, comparing 5.7.0-0.rc2 against 5.6 kernel, on 4 NUMA
> > server with 2x AMD 7351 CPU, we see performance degradation 22% for 32
> > threads (the system has 64 CPUs in total). We observe this degradation
> > only when we run a single SPECjbb binary. When running 4 SPECjbb
> > binaries in parallel, there is no change in performance between 5.6
> > and 5.7.
> >
>
> Minimally I suggest confirming that it's really due to
> adjust_numa_imbalance() by making the function a no-op and retesting.
> I have found odd artifacts with it but I'm unsure how to proceed without
> causing problems elsehwere.
>
> For example, netperf on localhost in some cases reported a regression
> when the client and server were running on the same node. The problem
> appears to be that netserver completes its work faster when running
> local and goes idle more regularly. The cost of going idle and waking up
> builds up and a lower throughput is reported but I'm not sure if gaming
> an artifact like that is a good idea.
>
> > That's why we are asking for the kernel tunable, which we would add to
> > the tuned profile. We don't expect users to change this frequently but
> > rather to set the performance profile once based on the purpose of the
> > server.
> >
> > If you could prepare a patch for us, we would be more than happy to
> > test it extensively. Based on the results, we can then evaluate if
> > it's the way to go. Thoughts?
> >
>
> I would suggest simply disabling that function first to ensure that is
> really what is causing problems for you.
>
> --
> Mel Gorman
> SUSE Labs
>


-- 
-Jirka