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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Dave Chinner <dgc@kernel.org>
Cc: Marco Crivellari <marco.crivellari@suse.com>,
	linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
	Tejun Heo <tj@kernel.org>, Lai Jiangshan <jiangshanlai@gmail.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Michal Hocko <mhocko@suse.com>,
	Anthony Iliopoulos <ailiopoulos@suse.com>,
	Carlos Maiolino <cem@kernel.org>
Subject: Re: [PATCH] xfs: convert alloc_workqueue users to WQ_UNBOUND
Message-ID: <20260219072556.Bpnr4F5x@linutronix.de>
References: <20260218165609.378983-1-marco.crivellari@suse.com>
 <aZZmVuY6C8PJMh_F@dread>
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In-Reply-To: <aZZmVuY6C8PJMh_F@dread>

On 2026-02-19 12:24:38 [+1100], Dave Chinner wrote:
> > The changes from per-cpu to unbound will help to improve situations where
> > CPU isolation is used, because unbound work can be moved away from
> > isolated CPUs.
> 
> If you are running operations through the XFS filesystem on isolated
> CPUs, then you absolutely need some of these the per-cpu workqueues
> running on those isolated CPUs too.
> 
> Also, these workqueues are typically implemented these ways to meet
> performancei targets, concurrency constraints or algorithm
> requirements. Changes like this need a bunch of XFS metadata
> scalability benchmarks on high end server systems under a variety of
> conditions to at least show there aren't any obvious any behavioural
> or performance regressions that result from the change.

So all of those (below) where you say "performance critical", those
work items are only enqueued from an interrupt? Never origin from a user
task?

Sebastian