linux-kernel - Re: Hard and soft lockups with FIO and LTP runs on a large system

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Message-ID: <Zpfye9DcmmB5JB38@ed.ac.uk>
Date: Wed, 17 Jul 2024 17:34:03 +0100
From: Karim Manaouil <kmanaouil.dev@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Bharata B Rao <bharata@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, nikunj@....com,
	"Upadhyay, Neeraj" <Neeraj.Upadhyay@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>, willy@...radead.org,
	yuzhao@...gle.com, kinseyho@...gle.com,
	Mel Gorman <mgorman@...e.de>, Mateusz Guzik <mjguzik@...il.com>
Subject: Re: Hard and soft lockups with FIO and LTP runs on a large system

On Wed, Jul 17, 2024 at 11:42:31AM +0200, Vlastimil Babka wrote:
> Seems to me it could be (except that ZONE_DMA corner case) a general
> scalability issue in that you tweak some part of the kernel and the
> contention moves elsewhere. At least in MM we have per-node locks so this
> means 256 CPUs per lock? It used to be that there were not that many
> (cores/threads) per a physical CPU and its NUMA node, so many cpus would
> mean also more NUMA nodes where the locks contention would distribute among
> them. I think you could try fakenuma to create these nodes artificially and
> see if it helps for the MM part. But if the contention moves to e.g. an
> inode lock, I'm not sure what to do about that then.

AMD EPYC BIOSes have an option called NPS (Nodes Per Socket) that can be
set to 1, 2, 4 or 8 and that divides the system up into the chosen number
of NUMA nodes.

Karim
PhD Student
Edinburgh University