RE: [Intel-wired-lan] [PATCH v2] e1000e: Fix TX dispatch condition

[G, GurucharanX]

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@xxxxxxxxxx> On Behalf Of
> Akihiko Odaki
> Sent: Friday, October 28, 2022 6:30 PM
> Cc: Paul Menzel <pmenzel@xxxxxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Yuri Benditovich
> <yuri.benditovich@xxxxxxxxxx>; Eric Dumazet <edumazet@xxxxxxxxxx>;
> intel-wired-lan@xxxxxxxxxxxxxxxx; Yan Vugenfirer <yan@xxxxxxxxxx>; Jakub
> Kicinski <kuba@xxxxxxxxxx>; Paolo Abeni <pabeni@xxxxxxxxxx>; David S .
> Miller <davem@xxxxxxxxxxxxx>
> Subject: [Intel-wired-lan] [PATCH v2] e1000e: Fix TX dispatch condition
> 
> 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@xxxxxxxxxx>
> ---
>  drivers/net/ethernet/intel/e1000e/netdev.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 

Tested-by: Gurucharan <gurucharanx.g@xxxxxxxxx> (A Contingent worker at Intel)