netdev - Re: [PATCH net 1/3] virtio-net: make refill work a per receive queue work

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Message-ID: <CACGkMEs7_-=-8w=7gW8R_EhzfWOwuDoj4p-iCPQ7areOa9uaUw@mail.gmail.com>
Date: Thu, 25 Dec 2025 15:33:29 +0800
From: Jason Wang <jasowang@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org, 
	Eugenio Pérez <eperezma@...hat.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	Stanislav Fomichev <sdf@...ichev.me>, virtualization@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Bui Quang Minh <minhquangbui99@...il.com>
Subject: Re: [PATCH net 1/3] virtio-net: make refill work a per receive queue work

On Wed, Dec 24, 2025 at 9:48 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Wed, Dec 24, 2025 at 09:37:14AM +0800, Xuan Zhuo wrote:
> >
> > Hi Jason,
> >
> > I'm wondering why we even need this refill work. Why not simply let NAPI retry
> > the refill on its next run if the refill fails? That would seem much simpler.
> > This refill work complicates maintenance and often introduces a lot of
> > concurrency issues and races.
> >
> > Thanks.
>
> refill work can refill from GFP_KERNEL, napi only from ATOMIC.
>
> And if GFP_ATOMIC failed, aggressively retrying might not be a great idea.

Btw, I see some drivers are doing things as Xuan said. E.g
mlx5e_napi_poll() did:

busy |= INDIRECT_CALL_2(rq->post_wqes,
                                mlx5e_post_rx_mpwqes,
                                mlx5e_post_rx_wqes,

...

if (busy) {
         if (likely(mlx5e_channel_no_affinity_change(c))) {
                work_done = budget;
                goto out;
...

>
> Not saying refill work is a great hack, but that is the reason for it.
> --
> MST
>

Thanks