netdev - Re: [rfc net-next v6 2/3] virtio

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Message-ID: <874nl5yn4k.fsf@rustcorp.com.au>
Date:	Mon, 05 Nov 2012 09:46:58 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Jason Wang <jasowang@...hat.com>, mst@...hat.com,
	davem@...emloft.net, virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	krkumar2@...ibm.com
Cc:	kvm@...r.kernel.org, Jason Wang <jasowang@...hat.com>
Subject: Re: [rfc net-next v6 2/3] virtio_net: multiqueue support

Jason Wang <jasowang@...hat.com> writes:
> This addes multiqueue support to virtio_net driver. There's two mode supported:
> single queue pair mode and multiple queue pairs mode. An obvious
> difference compared with a physical mq card is that virtio-net reserve
> first two virtqueues when it is working in multiqueue mode, this is
> used for implementing adaptive mode switching in the future. The
> virtqueues that were in both mq and sq mode were initialized and only
> one queue pair (single queue mode) were used at default. User could
> use ethtool -L to switch to multiqueue mode withe the next patch.

Hi Jason,

        This first patch looks good, but conflates three things
together:
(1) Separate per-queue structures from struct virtnet_info to allow
    multiple queues.  This is the mechanical part of the patch.
(2) An annotation bugfix, see below.
(3) Enabling mq using a new feature and negotiation.

> @@ -700,7 +767,8 @@ static struct rtnl_link_stats64 *virtnet_stats(struct net_device *dev,
>  	unsigned int start;
>  
>  	for_each_possible_cpu(cpu) {
> -		struct virtnet_stats *stats = per_cpu_ptr(vi->stats, cpu);
> +		struct virtnet_stats __percpu *stats
> +			= per_cpu_ptr(vi->stats, cpu);
>  		u64 tpackets, tbytes, rpackets, rbytes;
>  
>  		do {

Cheers,
Rusty.
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