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Date: Wed, 19 Mar 2025 07:26:57 -1000
From: Tejun Heo <tj@kernel.org>
To: Mateusz Guzik <mjguzik@gmail.com>
Cc: Greg Thelen <gthelen@google.com>, Johannes Weiner <hannes@cmpxchg.org>,
	Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Eric Dumazet <edumzaet@google.com>,
	Yosry Ahmed <yosryahmed@google.com>, cgroups@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Eric Dumazet <edumazet@google.com>
Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu)
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References: <20250319071330.898763-1-gthelen@google.com>
 <u5kcjffhyrjsxagpdzas7q463ldgqtptaafozea3bv64odn2xt@agx42ih5m76l>
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On Wed, Mar 19, 2025 at 11:47:32AM +0100, Mateusz Guzik wrote:
...
> Is not this going a little too far?
> 
> the lock + irq trip is quite expensive in its own right and now is
> going to be paid for each cpu, as in the total time spent executing
> cgroup_rstat_flush_locked is going to go up.

Lock/unlock when the cacheline is already on the cpu is pretty cheap and on
modern x86 cpus at least irq on/off are also only a few cycles, so you
probably wouldn't be able to tell the difference.

Thanks.

-- 
tejun