Re: [PATCH 2/2] xennet: fix TX doorbell coalescing — More flag dropped at NBL boundaries

[Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>]

On 17/09/2026 17:43, david ambu wrote:
>    __TransmitterSendNetBufferList computed the More flag as
>    (NET_BUFFER_NEXT_NB(NetBuffer) != NULL), which only looks at remaining
>    NET_BUFFERs within the current NBL. This evaluates to FALSE for the last
>    NB of every NBL, even when the outer loop in TransmitterSendNetBufferLists
>    still has additional NBLs to submit in the same batch.
> 
> Assisted-by: ClaudeCode:claude-opus-4.8
> Signed-off-by: david ambu <david.preetham@xxxxxxxxxx>

Please don't use the Unicode '—' in the commit message.

> ---
>   src/xennet/transmitter.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/src/xennet/transmitter.c b/src/xennet/transmitter.c
> index 4bb82bc..e17d89f 100644
> --- a/src/xennet/transmitter.c
> +++ b/src/xennet/transmitter.c
> @@ -288,7 +288,8 @@ __TransmitterHash(
>   static VOID
>   __TransmitterSendNetBufferList(
>       IN  PXENNET_TRANSMITTER     Transmitter,
> -    IN  PNET_BUFFER_LIST        NetBufferList
> +    IN  PNET_BUFFER_LIST        NetBufferList,
> +    IN  BOOLEAN                 MoreNbls
>       )
>   {
>       PNET_BUFFER_LIST_RESERVED   ListReserved;
> @@ -338,7 +339,7 @@ __TransmitterSendNetBufferList(
>                                   MaximumSegmentSize,
>                                   TagControlInformation,
>                                   &Hash,
> -                                (NetBufferListNext != NULL) ? TRUE : FALSE,
> +                                (NetBufferListNext != NULL || MoreNbls) ? 
> TRUE : FALSE,
>                                   Cookie);
>           }
>           else
> @@ -384,7 +385,9 @@ TransmitterSendNetBufferLists(
>           ListNext = NET_BUFFER_LIST_NEXT_NBL(NetBufferList);
>           NET_BUFFER_LIST_NEXT_NBL(NetBufferList) = NULL;
>   
> -        __TransmitterSendNetBufferList(Transmitter, NetBufferList);
> +        __TransmitterSendNetBufferList(Transmitter,
> +                                       NetBufferList,
> +                                       (ListNext != NULL) ? TRUE : FALSE);
>   
>           NetBufferList = ListNext;
>       }



--
Ngoc Tu Dinh | Vates XCP-ng Developer

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