netdev - RE: [Intel-wired-lan] [PATCH iwl-next v5 02/13] idpf: fix Rx descriptor ready check barrier in splitq

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Message-ID: <DM4PR11MB64551BDC0C6DE8AA57C4542B9800A@DM4PR11MB6455.namprd11.prod.outlook.com>
Date: Thu, 4 Sep 2025 16:43:24 +0000
From: "R, Ramu" <ramu.r@...el.com>
To: "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
CC: "Lobakin, Aleksander" <aleksander.lobakin@...el.com>, "Kubiak, Michal"
	<michal.kubiak@...el.com>, "Fijalkowski, Maciej"
	<maciej.fijalkowski@...el.com>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, "Kitszel, Przemyslaw"
	<przemyslaw.kitszel@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David
 S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, "Jakub
 Kicinski" <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Alexei
 Starovoitov" <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, "Simon
 Horman" <horms@...nel.org>, NXNE CNSE OSDT ITP Upstreaming
	<nxne.cnse.osdt.itp.upstreaming@...el.com>, "bpf@...r.kernel.org"
	<bpf@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Intel-wired-lan] [PATCH iwl-next v5 02/13] idpf: fix Rx
 descriptor ready check barrier in splitq

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of
> Alexander Lobakin
> Sent: Tuesday, August 26, 2025 9:25 PM
> To: intel-wired-lan@...ts.osuosl.org
> Cc: Lobakin, Aleksander <aleksander.lobakin@...el.com>; Kubiak, Michal
> <michal.kubiak@...el.com>; Fijalkowski, Maciej
> <maciej.fijalkowski@...el.com>; Nguyen, Anthony L
> <anthony.l.nguyen@...el.com>; Kitszel, Przemyslaw
> <przemyslaw.kitszel@...el.com>; Andrew Lunn <andrew+netdev@...n.ch>;
> David S. Miller <davem@...emloft.net>; Eric Dumazet
> <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>; Paolo Abeni
> <pabeni@...hat.com>; Alexei Starovoitov <ast@...nel.org>; Daniel
> Borkmann <daniel@...earbox.net>; Simon Horman <horms@...nel.org>;
> NXNE CNSE OSDT ITP Upstreaming
> <nxne.cnse.osdt.itp.upstreaming@...el.com>; bpf@...r.kernel.org;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: [Intel-wired-lan] [PATCH iwl-next v5 02/13] idpf: fix Rx descriptor
> ready check barrier in splitq
> 
> No idea what the current barrier position was meant for. At that point,
> nothing is read from the descriptor, only the pointer to the actual one is
> fetched.
> The correct barrier usage here is after the generation check, so that only the
> first qword is read if the descriptor is not yet ready and we need to stop
> polling. Debatable on coherent DMA as the Rx descriptor size is <= cacheline
> size, but anyway, the current barrier position only makes the codegen worse.
> 
> Fixes: 3a8845af66ed ("idpf: add RX splitq napi poll support")
> Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> ---
>  drivers/net/ethernet/intel/idpf/idpf_txrx.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
Tested-by: R,Ramu <ramu.r@...el.com>