netdev - Re: [PATCH net-next v3] virtio_net: add support for Byte Queue Limits

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Message-ID: <20240814053637-mutt-send-email-mst@kernel.org>
Date: Wed, 14 Aug 2024 05:43:51 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>, netdev@...r.kernel.org,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, jasowang@...hat.com, xuanzhuo@...ux.alibaba.com,
	virtualization@...ts.linux.dev, ast@...nel.org,
	daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
	dave.taht@...il.com, kerneljasonxing@...il.com,
	hengqi@...ux.alibaba.com
Subject: Re: [PATCH net-next v3] virtio_net: add support for Byte Queue Limits

On Wed, Aug 14, 2024 at 10:17:15AM +0200, Jiri Pirko wrote:
> >diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> >index 3f10c72743e9..c6af18948092 100644
> >--- a/drivers/net/virtio_net.c
> >+++ b/drivers/net/virtio_net.c
> >@@ -2867,8 +2867,8 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
> > 	if (err < 0)
> > 		goto err_xdp_reg_mem_model;
> > 
> >-	virtnet_napi_enable(vi->rq[qp_index].vq, &vi->rq[qp_index].napi);
> > 	netdev_tx_reset_queue(netdev_get_tx_queue(vi->dev, qp_index));
> >+	virtnet_napi_enable(vi->rq[qp_index].vq, &vi->rq[qp_index].napi);
> > 	virtnet_napi_tx_enable(vi, vi->sq[qp_index].vq, &vi->sq[qp_index].napi);
> 
> Hmm, I have to look at this a bit more. I think this might be accidental
> fix. The thing is, napi can be triggered even if it is disabled:
> 
>        ->__local_bh_enable_ip()
>          -> net_rx_action()
>            -> __napi_poll()
> 
> Here __napi_poll() calls napi_is_scheduled() and calls virtnet_poll_tx()
> in case napi is scheduled. napi_is_scheduled() checks NAPI_STATE_SCHED
> bit in napi state.
> 
> However, this bit is set previously by netif_napi_add_weight().

It's actually set in napi_disable too, isn't it?

> 
> >
> > > ...
> >
> >Best regards
> >-- 
> >Marek Szyprowski, PhD
> >Samsung R&D Institute Poland
> >
> 
> 
> > 
> > 	return 0;
> >
> >
> >Will submit the patch in a jiff. Thanks!
> >
> >
> >
> >>
> >>Best regards
> >>-- 
> >>Marek Szyprowski, PhD
> >>Samsung R&D Institute Poland
> >>