linux-kernel - [LSF/MM/BPF TOPIC] Weighted interleave auto-tuning

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Message-Id: <20250109185048.28587-1-joshua.hahnjy@gmail.com>
Date: Thu,  9 Jan 2025 13:50:48 -0500
From: Joshua Hahn <joshua.hahnjy@...il.com>
To: lsf-pc@...ts.linux-foundation.org
Cc: Joshua Hahn <joshua.hahnjy@...il.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	gourry@...rry.net,
	ying.huang@...ux.alibaba.com,
	hyeonggon.yoo@...com,
	honggyu.kim@...com,
	kernel-team@...a.com
Subject: [LSF/MM/BPF TOPIC] Weighted interleave auto-tuning

Hello everyone, I hope everyone has had a great start to 2025!

Recently, I have been working on a patch series [1] with
Gregory Price <gourry@...rry.net> that provides new default interleave
weights, along with dynamic re-weighting on hotplug events and a series
of UAPIs that allow users to configure how they want the defaults to behave.

In introducing these new defaults, discussions have opened up in the
community regarding how best to create a UAPI that can provide
coherent and transparent interactions for the user. In particular, consider
this scenario: when a hotplug event happens and a node comes online
with new bandwidth information (and therefore changing the bandwidth
distributions across the system), should user-set weights be overwritten
to reflect the new distributions? If so, how can we justify overwriting
user-set values in a sysfs interface? If not, how will users manually
adjust the node weights to the optimal weight?

I would like to revisit some of the design choices made for this patch,
including how the defaults were derived, and open the conversation to
hear what the community believes is a reasonable way to allow users to
tune weighted interleave weights. More broadly, I hope to get gather
community insight on how they use weighted interleave, and do my best to
reflect those workflows in the patch.

Of course, I would also love to hear your thoughts about this topic
in this thread, or in the RFC thread (attached) as well. Have a great day!
Joshua

[1] https://lore.kernel.org/all/20241219191845.3506370-1-joshua.hahnjy@gmail.com/