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Message-ID: <20180104201934-mutt-send-email-mst@kernel.org>
Date: Thu, 4 Jan 2018 20:22:08 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Baron <jbaron@...mai.com>
Cc: davem@...emloft.net, jasowang@...hat.com, netdev@...r.kernel.org,
virtualization@...ts.linux-foundation.org, qemu-devel@...gnu.org,
virtio-dev@...ts.oasis-open.org
Subject: Re: [PATCH net-next v3 1/3] virtio_net: propagate linkspeed/duplex
settings from the hypervisor
On Thu, Jan 04, 2018 at 01:12:30PM -0500, Jason Baron wrote:
>
>
> On 01/04/2018 12:05 PM, Michael S. Tsirkin wrote:
> > On Thu, Jan 04, 2018 at 12:16:44AM -0500, Jason Baron wrote:
> >> The ability to set speed and duplex for virtio_net is useful in various
> >> scenarios as described here:
> >>
> >> 16032be virtio_net: add ethtool support for set and get of settings
> >>
> >> However, it would be nice to be able to set this from the hypervisor,
> >> such that virtio_net doesn't require custom guest ethtool commands.
> >>
> >> Introduce a new feature flag, VIRTIO_NET_F_SPEED_DUPLEX, which allows
> >> the hypervisor to export a linkspeed and duplex setting. The user can
> >> subsequently overwrite it later if desired via: 'ethtool -s'.
> >>
> >> Note that VIRTIO_NET_F_SPEED_DUPLEX is defined as bit 63, the intention
> >> is that device feature bits are to grow down from bit 63, since the
> >> transports are starting from bit 24 and growing up.
> >>
> >> Signed-off-by: Jason Baron <jbaron@...mai.com>
> >> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> >> Cc: Jason Wang <jasowang@...hat.com>
> >> Cc: virtio-dev@...ts.oasis-open.org
> >> ---
> >> drivers/net/virtio_net.c | 19 ++++++++++++++++++-
> >> include/uapi/linux/virtio_net.h | 13 +++++++++++++
> >> 2 files changed, 31 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> >> index 6fb7b65..0b2d314 100644
> >> --- a/drivers/net/virtio_net.c
> >> +++ b/drivers/net/virtio_net.c
> >> @@ -2146,6 +2146,22 @@ static void virtnet_config_changed_work(struct work_struct *work)
> >>
> >> vi->status = v;
> >>
> >> + if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_SPEED_DUPLEX)) {
> >
> > BTW we can avoid this read for when link goes down.
> > Not a big deal but still.
>
> So you are saying that we can just set vi->speed and vi->duplex to
> 'unknown' when the link goes down and not check for the presence of
> VIRTIO_NET_F_SPEED_DUPLEX?
>
> If so, that could over-write what the user may have configured in the
> guest via 'ethtool -s' when the link goes down, so that would be a
> change in behavior, but perhaps that is ok?
No - what I am saying is that your patch overwrites the values
set by user when link goes down.
I suggest limiting this call to when
if (vi->status & VIRTIO_NET_S_LINK_UP)
and then the values are overwritten when link goes up
which seems closer to what a user might expect.
>
> I think I would prefer to have the link down event still check for
> VIRTIO_NET_F_SPEED_DUPLEX before changing speed/duplex. That way we
> still have 2 modes for updating the fields:
>
> 1) completely guest controlled. Same as we have now and host does not
> change any values and does not set VIRTIO_NET_F_SPEED_DUPLEX flag (hence
> don't remove above check).
>
> 2) if speed or duplex or speed is set in the qemu command line, then set
> the VIRTIO_NET_F_SPEED_DUPLEX and have host control the settings of
> speed/duplex (with ability of guest to over-write if it wanted to).
>
>
> >
> >> + u32 speed;
> >> + u8 duplex;
> >> +
> >> + speed = virtio_cread32(vi->vdev,
> >> + offsetof(struct virtio_net_config,
> >> + speed));
> >> + if (ethtool_validate_speed(speed))
> >> + vi->speed = speed;
> >> + duplex = virtio_cread8(vi->vdev,
> >> + offsetof(struct virtio_net_config,
> >> + duplex));
> >> + if (ethtool_validate_duplex(duplex))
> >> + vi->duplex = duplex;
> >> + }
> >> +
> >> if (vi->status & VIRTIO_NET_S_LINK_UP) {
> >> netif_carrier_on(vi->dev);
> >> netif_tx_wake_all_queues(vi->dev);
> >
> > OK so this handles the case when VIRTIO_NET_F_STATUS is set,
> > but when it's clear we need to call this from virtnet_probe.
> >
> > I propose moving this chunk to a function and calling from two places.
> >
>
> good point. will update.
>
> Thanks,
>
> -Jason
>
> >
> >> @@ -2796,7 +2812,8 @@ static struct virtio_device_id id_table[] = {
> >> VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN, \
> >> VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
> >> VIRTIO_NET_F_CTRL_MAC_ADDR, \
> >> - VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
> >> + VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \
> >> + VIRTIO_NET_F_SPEED_DUPLEX
> >>
> >> static unsigned int features[] = {
> >> VIRTNET_FEATURES,
> >> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> >> index fc353b5..5de6ed3 100644
> >> --- a/include/uapi/linux/virtio_net.h
> >> +++ b/include/uapi/linux/virtio_net.h
> >> @@ -57,6 +57,8 @@
> >> * Steering */
> >> #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */
> >>
> >> +#define VIRTIO_NET_F_SPEED_DUPLEX 63 /* Device set linkspeed and duplex */
> >> +
> >> #ifndef VIRTIO_NET_NO_LEGACY
> >> #define VIRTIO_NET_F_GSO 6 /* Host handles pkts w/ any GSO type */
> >> #endif /* VIRTIO_NET_NO_LEGACY */
> >> @@ -76,6 +78,17 @@ struct virtio_net_config {
> >> __u16 max_virtqueue_pairs;
> >> /* Default maximum transmit unit advice */
> >> __u16 mtu;
> >> + /*
> >> + * speed, in units of 1Mb. All values 0 to INT_MAX are legal.
> >> + * Any other value stands for unknown.
> >> + */
> >> + __u32 speed;
> >> + /*
> >> + * 0x00 - half duplex
> >> + * 0x01 - full duplex
> >> + * Any other value stands for unknown.
> >> + */
> >> + __u8 duplex;
> >> } __attribute__((packed));
> >>
> >> /*
> >> --
> >> 2.6.1
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