linux-kernel - Re: [PATCH net-next v7 0/5] net: devmem: improve cpu cost of RX token management

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Message-ID: <CAHS8izPm22VoGCv93q=_nGhqOUR3R0JzVpYW6u0EJVxJJB-5Ag@mail.gmail.com>
Date: Tue, 9 Dec 2025 11:55:07 -0800
From: Mina Almasry <almasrymina@...gle.com>
To: Bobby Eshleman <bobbyeshleman@...il.com>
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>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, Willem de Bruijn <willemb@...gle.com>, 
	Neal Cardwell <ncardwell@...gle.com>, David Ahern <dsahern@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Jonathan Corbet <corbet@....net>, Andrew Lunn <andrew+netdev@...n.ch>, Shuah Khan <shuah@...nel.org>, 
	Donald Hunter <donald.hunter@...il.com>, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	Stanislav Fomichev <sdf@...ichev.me>, Bobby Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next v7 0/5] net: devmem: improve cpu cost of RX token management

On Tue, Dec 9, 2025 at 11:52 AM Bobby Eshleman <bobbyeshleman@...il.com> wrote:
>
> On Wed, Nov 19, 2025 at 07:37:07PM -0800, Bobby Eshleman wrote:
> > This series improves the CPU cost of RX token management by adding an
> > attribute to NETDEV_CMD_BIND_RX that configures sockets using the
> > binding to avoid the xarray allocator and instead use a per-binding niov
> > array and a uref field in niov.
> >
> > Improvement is ~13% cpu util per RX user thread.
> >
> > Using kperf, the following results were observed:
> >
> > Before:
> >       Average RX worker idle %: 13.13, flows 4, test runs 11
> > After:
> >       Average RX worker idle %: 26.32, flows 4, test runs 11
> >
> > Two other approaches were tested, but with no improvement. Namely, 1)
> > using a hashmap for tokens and 2) keeping an xarray of atomic counters
> > but using RCU so that the hotpath could be mostly lockless. Neither of
> > these approaches proved better than the simple array in terms of CPU.
> >
> > The attribute NETDEV_A_DMABUF_AUTORELEASE is added to toggle the
> > optimization. It is an optional attribute and defaults to 0 (i.e.,
> > optimization on).
> >
>
> [...]
> >
> > Changes in v7:
> > - use netlink instead of sockopt (Stan)
> > - restrict system to only one mode, dmabuf bindings can not co-exist
> >   with different modes (Stan)
> > - use static branching to enforce single system-wide mode (Stan)
> > - Link to v6: https://lore.kernel.org/r/20251104-scratch-bobbyeshleman-devmem-tcp-token-upstream-v6-0-ea98cf4d40b3@meta.com
> >
>
> Mina, I was wondering if you had any feedback on this approach?
>

Sorry for the delay, I'll take a look shortly.


-- 
Thanks,
Mina