linux-kernel - Re: [PATCH net-next] netfilter: conntrack: Reduce cond_resched frequency in gc

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Message-ID: <aO5K4mICGHVNlkHJ@strlen.de>
Date: Tue, 14 Oct 2025 15:06:42 +0200
From: Florian Westphal <fw@...len.de>
To: lirongqing <lirongqing@...du.com>
Cc: Pablo Neira Ayuso <pablo@...filter.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>, Phil Sutter <phil@....cc>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] netfilter: conntrack: Reduce cond_resched
 frequency in gc_worker

lirongqing <lirongqing@...du.com> wrote:
> From: Li RongQing <lirongqing@...du.com>
> 
> The current implementation calls cond_resched() in every iteration
> of the garbage collection loop. This creates some overhead when
> processing large conntrack tables with billions of entries,
> as each cond_resched() invocation involves scheduler operations.
> 
> To reduce this overhead, implement a time-based throttling mechanism
> that calls cond_resched() at most once per millisecond. This maintains
> system responsiveness while minimizing scheduler contention.
> 
> gc_worker() with hashsize=10000 shows measurable improvement:
> 
> Before: 7114.274us
> After:  5993.518us (15.8% reduction)

I dislike this, I have never seen this pattern.

Whole point of cond_resched() is to let scheduler decide.

Maybe it would be better to move gc_worker off to its own
work queue (create_workqueue()) instead of reusing system wq
so one can tune the priority instead?