linux-kernel - Re: [Intel-wired-lan] [PATCH v2] e1000e: Fix TX dispatch condition

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Date:   Thu, 10 Nov 2022 11:55:25 +0200
From:   "naamax.meir" <naamax.meir@...ux.intel.com>
To:     Akihiko Odaki <akihiko.odaki@...nix.com>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Yuri Benditovich <yuri.benditovich@...nix.com>,
        Eric Dumazet <edumazet@...gle.com>,
        intel-wired-lan@...ts.osuosl.org, Yan Vugenfirer <yan@...nix.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH v2] e1000e: Fix TX dispatch condition

On 10/28/2022 16:00, Akihiko Odaki wrote:
> e1000_xmit_frame is expected to stop the queue and dispatch frames to
> hardware if there is not sufficient space for the next frame in the
> buffer, but sometimes it failed to do so because the estimated maxmium
> size of frame was wrong. As the consequence, the later invocation of
> e1000_xmit_frame failed with NETDEV_TX_BUSY, and the frame in the buffer
> remained forever, resulting in a watchdog failure.
> 
> This change fixes the estimated size by making it match with the
> condition for NETDEV_TX_BUSY. Apparently, the old estimation failed to
> account for the following lines which determines the space requirement
> for not causing NETDEV_TX_BUSY:
>      ```
>      	/* reserve a descriptor for the offload context */
>      	if ((mss) || (skb->ip_summed == CHECKSUM_PARTIAL))
>      		count++;
>      	count++;
> 
>      	count += DIV_ROUND_UP(len, adapter->tx_fifo_limit);
>      ```
> 
> This issue was found when running http-stress02 test included in Linux
> Test Project 20220930 on QEMU with the following commandline:
> ```
> qemu-system-x86_64 -M q35,accel=kvm -m 8G -smp 8
> 	-drive if=virtio,format=raw,file=root.img,file.locking=on
> 	-device e1000e,netdev=netdev
> 	-netdev tap,script=ifup,downscript=no,id=netdev
> ```
> 
> Fixes: bc7f75fa9788 ("[E1000E]: New pci-express e1000 driver (currently for ICH9 devices only)")
> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
>   drivers/net/ethernet/intel/e1000e/netdev.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
Tested-by: Naama Meir <naamax.meir@...ux.intel.com>