Re: [PATCH v6 0/2] Adjust NUMA imbalance for multiple LLCs

From: Peter Zijlstra <peterz@infradead.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Ingo Molnar <mingo@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	Barry Song <song.bao.hua@hisilicon.com>,
	Mike Galbraith <efault@gmx.de>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	Gautham Shenoy <gautham.shenoy@amd.com>,
	K Prateek Nayak <kprateek.nayak@amd.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v6 0/2] Adjust NUMA imbalance for multiple LLCs
Date: Wed, 9 Feb 2022 10:38:28 +0100	[thread overview]
Message-ID: <20220209093828.GL23216@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20220208094334.16379-1-mgorman@techsingularity.net>

On Tue, Feb 08, 2022 at 09:43:32AM +0000, Mel Gorman wrote:
> Changelog sinve v5
> o Fix off-by-one error
> 
> Changelog since V4
> o Scale imbalance based on the top domain that prefers siblings
> o Keep allowed imbalance as 2 up to the point where LLCs can be overloaded
> 
> Changelog since V3
> o Calculate imb_numa_nr for multiple SD_NUMA domains
> o Restore behaviour where communicating pairs remain on the same node
> 
> Commit 7d2b5dd0bcc4 ("sched/numa: Allow a floating imbalance between NUMA
> nodes") allowed an imbalance between NUMA nodes such that communicating
> tasks would not be pulled apart by the load balancer. This works fine when
> there is a 1:1 relationship between LLC and node but can be suboptimal
> for multiple LLCs if independent tasks prematurely use CPUs sharing cache.
> 
> The series addresses two problems -- inconsistent logic when allowing a
> NUMA imbalance and sub-optimal performance when there are many LLCs per
> NUMA node.
> 
>  include/linux/sched/topology.h |  1 +
>  kernel/sched/fair.c            | 30 ++++++++++---------
>  kernel/sched/topology.c        | 53 ++++++++++++++++++++++++++++++++++
>  3 files changed, 71 insertions(+), 13 deletions(-)

Thanks!