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From: Jason Xing <kerneljasonxing@gmail.com>
Date: Sun, 9 Jun 2024 12:47:23 +0800
Message-ID: <CAL+tcoDqyYy7mE6W8qvDJZgMK_4sYwXPzpidvgEu=r-uJ46k4Q@mail.gmail.com>
Subject: Re: [PATCH net-next v2] net: sysfs: Do not create sysfs for non BQL device
To: Breno Leitao <leitao@debian.org>
Cc: Eric Dumazet <edumazet@google.com>, Florian Fainelli <f.fainelli@gmail.com>, 
	Stephen Hemminger <stephen@networkplumber.org>, kuba@kernel.org, davem@davemloft.net, 
	pabeni@redhat.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, 
	horms@kernel.org, Johannes Berg <johannes.berg@intel.com>
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Hello Breno, Eric

On Mon, Feb 19, 2024 at 5:47=E2=80=AFPM Breno Leitao <leitao@debian.org> wr=
ote:
>
> On Fri, Feb 16, 2024 at 07:45:37PM +0100, Eric Dumazet wrote:
> > On Fri, Feb 16, 2024 at 7:41=E2=80=AFPM Florian Fainelli <f.fainelli@gm=
ail.com> wrote:
> > >
> > > On 2/16/24 09:29, Stephen Hemminger wrote:
> > > > On Fri, 16 Feb 2024 01:41:52 -0800
> > > > Breno Leitao <leitao@debian.org> wrote:
> > > >
> > > >> +static bool netdev_uses_bql(const struct net_device *dev)
> > > >> +{
> > > >> +    if (dev->features & NETIF_F_LLTX ||
> > > >> +        dev->priv_flags & IFF_NO_QUEUE)
> > > >> +            return false;
> > > >> +
> > > >> +    return IS_ENABLED(CONFIG_BQL);
> > > >> +}
> > > >
> > > > Various compilers will warn about missing parens in that expression=
.
> > > > It is valid but mixing & and || can be bug trap.
> > > >
> > > >       if ((dev->features & NETIF_F_LLTX) || (dev->priv_flags & IFF_=
NO_QUEUE))
> > > >               return false;
> > > >
> > > > Not all drivers will be using bql, it requires driver to have that =
code.
> > > > So really it means driver could be using BQL.
> > > > Not sure if there is a way to find out if driver has the required B=
QL bits.
> > >
> > > There is not a feature flag to be keying off if that is what you are
> > > after, you would need to audit the drivers and see whether they make
> > > calls to netdev_tx_sent_queue(), netdev_tx_reset_queue(),
> > > netdev_tx_completed_queue().
> > >
> > > I suppose you might be able to programmatically extract that informat=
ion
> > > by looking at whether a given driver object file has a reference to
> > > dql_{reset,avail,completed} or do that at the source level, whichever=
 is
> > > easier.
> >
> > Note that the suggested patch does not change current functionality.
> >
> > Traditionally, we had sysfs entries fpr BQL for all netdev, regardless =
of them
> > using BQL or not.
> >
> > The patch seems to be a good first step.
>
> Thanks Eric. I agree it solves the problem without creating a new
> feature flag, that could also be done, but maybe less important than
> this first step.

When I'm reading and testing the dqs codes in my VM, I realize that
the virtio_net driver should have been excluded from BQL drivers,
which means VM using virtio_net driver should not have the
/sys/class/net/eth1/queues/tx-1/byte_queue_limits directory because It
has neither NETIF_F_LLTX nor IFF_NO_QUEUE.

I'm trying to cook a patch to fix it without introducing a new feature
like NETIF_F_LOOPBACK, but I failed to have a good patch.

I have two options in my mind:
1) introduce a feature flag only for virtion_net [1]
2) introduce a BQL flag, and then apply it to all the drivers which
has either NETIF_F_LLTX or IFF_NO_QUEUE bit, including virtio_net
driver

Do you have any ideas or suggestions?

Thanks in advance!

[1]
untested patch for now:
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 61a57d134544..e39417d99ea8 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -5634,7 +5634,7 @@ static int virtnet_probe(struct virtio_device *vdev)
                           IFF_TX_SKB_NO_LINEAR;
        dev->netdev_ops =3D &virtnet_netdev;
        dev->stat_ops =3D &virtnet_stat_ops;
-       dev->features =3D NETIF_F_HIGHDMA;
+       dev->features =3D NETIF_F_HIGHDMA | NETIF_F_VIRTNET;

        dev->ethtool_ops =3D &virtnet_ethtool_ops;
        SET_NETDEV_DEV(dev, &vdev->dev);
diff --git a/include/linux/netdev_features.h b/include/linux/netdev_feature=
s.h
index 7c2d77d75a88..4ade9cdf079e 100644
--- a/include/linux/netdev_features.h
+++ b/include/linux/netdev_features.h
@@ -14,7 +14,7 @@ typedef u64 netdev_features_t;
 enum {
        NETIF_F_SG_BIT,                 /* Scatter/gather IO. */
        NETIF_F_IP_CSUM_BIT,            /* Can checksum TCP/UDP over IPv4. =
*/
-       __UNUSED_NETIF_F_1,
+       //__UNUSED_NETIF_F_1,
        NETIF_F_HW_CSUM_BIT,            /* Can checksum all the packets. */
        NETIF_F_IPV6_CSUM_BIT,          /* Can checksum TCP/UDP over IPV6 *=
/
        NETIF_F_HIGHDMA_BIT,            /* Can DMA to high memory. */
@@ -91,6 +91,7 @@ enum {
        NETIF_F_HW_HSR_FWD_BIT,         /* Offload HSR forwarding */
        NETIF_F_HW_HSR_DUP_BIT,         /* Offload HSR duplication */

+       NETIF_F_VIRTNET_BIT,            /* Enable virtnet */
        /*
         * Add your fresh new feature above and remember to update
         * netdev_features_strings[] in net/ethtool/common.c and maybe
@@ -122,6 +123,7 @@ enum {
 #define NETIF_F_IPV6_CSUM      __NETIF_F(IPV6_CSUM)
 #define NETIF_F_LLTX           __NETIF_F(LLTX)
 #define NETIF_F_LOOPBACK       __NETIF_F(LOOPBACK)
+#define NETIF_F_VIRTNET                __NETIF_F(VIRTNET)
 #define NETIF_F_LRO            __NETIF_F(LRO)
 #define NETIF_F_NETNS_LOCAL    __NETIF_F(NETNS_LOCAL)
 #define NETIF_F_NOCACHE_COPY   __NETIF_F(NOCACHE_COPY)
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 4c27a360c294..d52d95ea6fb6 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1764,7 +1764,7 @@ static const struct kobj_type netdev_queue_ktype =3D =
{

 static bool netdev_uses_bql(const struct net_device *dev)
 {
-       if (dev->features & NETIF_F_LLTX ||
+       if (dev->features & (NETIF_F_LLTX | NETIF_F_VIRTNET) ||
            dev->priv_flags & IFF_NO_QUEUE)
                return false;

diff --git a/net/ethtool/common.c b/net/ethtool/common.c
index 6b2a360dcdf0..efb39a185e4b 100644
--- a/net/ethtool/common.c
+++ b/net/ethtool/common.c
@@ -74,6 +74,7 @@ const char
netdev_features_strings[NETDEV_FEATURE_COUNT][ETH_GSTRING_LEN] =3D {
        [NETIF_F_HW_HSR_TAG_RM_BIT] =3D    "hsr-tag-rm-offload",
        [NETIF_F_HW_HSR_FWD_BIT] =3D       "hsr-fwd-offload",
        [NETIF_F_HW_HSR_DUP_BIT] =3D       "hsr-dup-offload",
+       [NETIF_F_VIRTNET_BIT] =3D         "virtnet",
 };

 const char

>
> Hoping this is OK, I am planning to send a v2 adding the extra
> parenthesis as reported above.
>
> Thanks
>