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Date:   Fri, 28 Oct 2022 12:01:10 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Akihiko Odaki <akihiko.odaki@...nix.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yuri Benditovich <yuri.benditovich@...nix.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Yan Vugenfirer <yan@...nix.com>,
        intel-wired-lan@...ts.osuosl.org, Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH] e1000e: Fix TX dispatch condition

Dear Akihiko,


Thank you very much for the patch.

Am 13.10.22 um 07:00 schrieb Akihiko Odaki:
> 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);

I’d just use Markdown syntax, and indent by four spaces without > for 
citation.

> This issue was found with http-stress02 test included in Linux Test
> Project 20220930.

So it was reproduced in QEMU? For convenience, it’d be great if you 
added the QEMU command.

Also, do you know if this is a regression? If so, it’d be great if you 
added the Fixes: tag.


Kind regards,

Paul


> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
>   drivers/net/ethernet/intel/e1000e/netdev.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
> index 321f2a95ae3a..da113f5011e9 100644
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> @@ -5936,9 +5936,9 @@ static netdev_tx_t e1000_xmit_frame(struct sk_buff *skb,
>   		e1000_tx_queue(tx_ring, tx_flags, count);
>   		/* Make sure there is space in the ring for the next send. */
>   		e1000_maybe_stop_tx(tx_ring,
> -				    (MAX_SKB_FRAGS *
> +				    ((MAX_SKB_FRAGS + 1) *
>   				     DIV_ROUND_UP(PAGE_SIZE,
> -						  adapter->tx_fifo_limit) + 2));
> +						  adapter->tx_fifo_limit) + 4));
>   
>   		if (!netdev_xmit_more() ||
>   		    netif_xmit_stopped(netdev_get_tx_queue(netdev, 0))) {

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