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

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Message-ID: <20251225112729-mutt-send-email-mst@kernel.org>
Date: Thu, 25 Dec 2025 11:27:43 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...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 Thu, Dec 25, 2025 at 03:33:29PM +0800, Jason Wang wrote:
> 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;
> ...


is busy a GFP_ATOMIC allocation failure?

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