linux-kernel - Re: [PATCH net-next v3 0/2] net: devmem: improve cpu cost of RX token management

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Message-ID: <aNbDNr8ZHw5AzVHQ@devvm11784.nha0.facebook.com>
Date: Fri, 26 Sep 2025 09:45:42 -0700
From: Bobby Eshleman <bobbyeshleman@...il.com>
To: Simon Horman <horms@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Stanislav Fomichev <sdf@...ichev.me>,
	Mina Almasry <almasrymina@...gle.com>,
	Bobby Eshleman <bobbyeshleman@...a.com>
Subject: Re: [PATCH net-next v3 0/2] net: devmem: improve cpu cost of RX
 token management

On Fri, Sep 26, 2025 at 04:55:01PM +0100, Simon Horman wrote:
> On Fri, Sep 26, 2025 at 08:02:52AM -0700, Bobby Eshleman wrote:
> > This series improves the CPU cost of RX token management by replacing
> > the xarray allocator with an niov array and a uref field in niov.
> > 
> > Improvement is ~5% per RX user thread.
> > 
> > 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.
> > 
> > Running with a NCCL workload is still TODO, but I will follow up on this
> > thread with those results when done.
> > 
> > Signed-off-by: Bobby Eshleman <bobbyeshleman@...a.com>
> 
> Hi Bobby,
> 
> Unfortunately this patchset doesn't apply cleanly to net-next.
> So you'll need to rebase and repost at some point.
> 
> -- 
> pw-bot: changes-requested

Got it, just resent and added this check to my automation, thanks!

Best,
Bobby