linux-kernel - Re: [PATCH net-next v2] net: devmem: convert binding refcount to percpu

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Message-ID: <aS9px07mgnNjSu8e@devvm11784.nha0.facebook.com>
Date: Tue, 2 Dec 2025 14:35:51 -0800
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: "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>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mina Almasry <almasrymina@...gle.com>,
	Stanislav Fomichev <sdf@...ichev.me>, asml.silence@...il.com,
	Bobby Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next v2] net: devmem: convert binding refcount to
 percpu_ref

On Tue, Dec 02, 2025 at 11:34:17AM -0800, Bobby Eshleman wrote:
> From: Bobby Eshleman <bobbyeshleman@...a.com>
> 
> Convert net_devmem_dmabuf_binding refcount from refcount_t to percpu_ref
> to optimize common-case reference counting on the hot path.
> 
> The typical devmem workflow involves binding a dmabuf to a queue
> (acquiring the initial reference on binding->ref), followed by
> high-volume traffic where every skb fragment acquires a reference.
> Eventually traffic stops and the unbind operation releases the initial
> reference. Additionally, the high traffic hot path is often multi-core.
> This access pattern is ideal for percpu_ref as the first and last
> reference during bind/unbind normally book-ends activity in the hot
> path.
> 
> __net_devmem_dmabuf_binding_free becomes the percpu_ref callback invoked
> when the last reference is dropped.
> 

My apologies for sending this out after net-next closed. Won't happen
again.

Best,
Bobby