From: Jakub Kicinski <kuba@kernel.org>
To: Jay Vosburgh <jay.vosburgh@canonical.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>,
netdev@vger.kernel.org, Jonathan Toppins <jtoppins@redhat.com>,
Veaceslav Falico <vfalico@gmail.com>,
Andy Gospodarek <andy@greyhouse.net>
Subject: Re: [PATCH net] veth: Add updating of trans_start
Date: Fri, 17 Jun 2022 17:55:50 -0700 [thread overview]
Message-ID: <20220617175550.6a3602ab@kernel.org> (raw)
In-Reply-To: <28607.1655512063@famine>
On Fri, 17 Jun 2022 17:27:43 -0700 Jay Vosburgh wrote:
> Jakub Kicinski <kuba@kernel.org> wrote:
> >On Fri, 17 Jun 2022 09:42:55 -0700 Jay Vosburgh wrote:
> >> In this case, it's to permit the bonding ARP / ND monitor to
> >> function if that software device (veth in this case) is added to a bond
> >> using the ARP / ND monitor (which relies on trans_start, and has done so
> >> since at least 2.6.0). I'll agree it's a niche case; this was broken
> >> for veth for quite some time, but veth + netns is handy for software
> >> only test cases, so it seems worth doing.
> >
> >I presume it needs it to check if the device has transmitted anything
> >in the last unit of time, can we look at the device stats for LLTX for
> >example?
>
> Yes, that's the use case.
>
> Hmm. Polling the device stats would likely work for software
> devices, although the unit of time varies (some checks are fixed at one
> unit, but others can be N units depending on the missed_max option
> setting).
>
> Polling hardware devices might not work; as I recall, some
> devices only update the statistics on timespans on the order of seconds,
> e.g., bnx2 and tg3 appear to update once per second. But those do
> update trans_start.
Right, unfortunately.
> The question then becomes how to distinguish a software LLTX
> device from a hardware LLTX device.
If my way of thinking about trans_start is correct then we can test
for presence of ndo_tx_timeout. Anything that has the tx_timeout NDO
must be maintaining trans_start.
> >> I didn't exhaustively check all LLTX drivers, but, e.g., tun
> >> does update trans_start:
> >>
> >> drivers/net/tun.c:
> >>
> >> /* NETIF_F_LLTX requires to do our own update of trans_start */
> >> queue = netdev_get_tx_queue(dev, txq);
> >> txq_trans_cond_update(queue);
> >
> >Well, it is _an_ example, but the only one I can find. And the
> >justification is the same as yours now -- make bonding work a31d27fb.
> >Because of that I don't think we can use tun as a proof that trans
> >start should be updated on LLTX devices as a general, stack-wide rule.
> >There's a lot more LLTX devices than veth and tun.
>
> I'm not suggesting that all (software) LLTX software devices be
> updated.
The ones which are not updated would remain broken then, no?
Waiting for someone to try to bond them and discover it doesn't work.
next prev parent reply other threads:[~2022-06-18 0:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-16 19:26 [PATCH net] veth: Add updating of trans_start Jay Vosburgh
2022-06-17 10:40 ` patchwork-bot+netdevbpf
2022-06-17 15:45 ` Jakub Kicinski
2022-06-17 16:42 ` Jay Vosburgh
2022-06-17 19:44 ` Jakub Kicinski
2022-06-18 0:27 ` Jay Vosburgh
2022-06-18 0:55 ` Jakub Kicinski [this message]
2022-06-21 19:52 ` Jakub Kicinski
2022-06-22 1:42 ` Jay Vosburgh
2022-06-22 4:38 ` Jakub Kicinski
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