linux-kernel - Re: [PATCH net-next v17 01/14] netdev: add netdev_rx_queue

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Message-ID: <CAHS8izMZQLsBWPXWiqPwaQHfupKc5VAuxW+6kpWmzi-vw8JEWQ@mail.gmail.com>
Date: Wed, 31 Jul 2024 17:19:11 -0400
From: Mina Almasry <almasrymina@...gle.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
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	Matt Turner <mattst88@...il.com>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
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	Andreas Larsson <andreas@...sler.com>, Jesper Dangaard Brouer <hawk@...nel.org>, 
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Subject: Re: [PATCH net-next v17 01/14] netdev: add netdev_rx_queue_restart()

On Tue, Jul 30, 2024 at 4:17 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> On Tue, 30 Jul 2024 02:26:05 +0000, Mina Almasry <almasrymina@...gle.com> wrote:
> > Add netdev_rx_queue_restart() function to netdev_rx_queue.h
>
>
> Can you say more? As far as I understand, we just release the buffer
> submitted to the rx ring and get a new page pool.
>

Yes, I just noticed that this commit message is underwritten. I'll add
more color. Maybe something like;

====
Add netdev_rx_queue_restart(), which resets an rx queue using the
queue API recently merged[1].

The queue API was merged to enable the core net stack reset individual
rx queues to actuate changes in the rx queue's configuration. In later
patches in this series, we will use netdev_rx_queue_restart() to reset
rx queues after binding or unbinding dmabuf configuration, which will
cause reallocation of the page_pool to repopulate its memory using the
new configuration.

[1] https://lore.kernel.org/netdev/20240430231420.699177-1-shailend@google.com/T/
====

> But I personally feel that the interface here is a bit too complicated. In
> particular, we also need to copy the rx struct memory, which means it is a
> dangerous operation for many pointers.
>

Understood, but the complication is necessary based on previous
discussions. Jakub requests that we must allocate memory for a new rx
queues before bringing down the existing queue, to guard against the
interface remaining down on ENOMEM error.

Btw, I notice the series was marked as changes requested; the only
feedback I got was this one and the incorrect netmem_priv.h header.
I'll fix and repost. It's just slightly weird because both v16 and v17
are marked as changes requested in patchwork.