RE: [PATCH net-next] hv_netvsc: Increase delay for RNDIS_STATUS_NETWORK_CHANGE

-----Original Message-----
From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
Sent: Wednesday, February 3, 2016 11:06 AM
To: Haiyang Zhang <haiyangz@microsoft.com>
Cc: davem@davemloft.net; netdev@vger.kernel.org; KY Srinivasan
[off-list ref]; olaf@aepfle.de; linux-kernel@vger.kernel.org;
driverdev-devel@linuxdriverproject.org
Subject: Re: [PATCH net-next] hv_netvsc: Increase delay for
RNDIS_STATUS_NETWORK_CHANGE

Haiyang Zhang [off-list ref] writes:

quoted

quoted

-----Original Message-----
From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
Sent: Wednesday, February 3, 2016 8:06 AM
To: Haiyang Zhang <haiyangz@microsoft.com>
Cc: davem@davemloft.net; netdev@vger.kernel.org; KY Srinivasan
[off-list ref]; olaf@aepfle.de; linux-kernel@vger.kernel.org;
driverdev-devel@linuxdriverproject.org
Subject: Re: [PATCH net-next] hv_netvsc: Increase delay for
RNDIS_STATUS_NETWORK_CHANGE

Haiyang Zhang [off-list ref] writes:

quoted

We simulates a link down period for

RNDIS_STATUS_NETWORK_CHANGE

quoted

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message to

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trigger DHCP renew. User daemons may need multiple seconds to

trigger

quoted

quoted

the

quoted

link down event. (e.g. ifplugd: 5sec, network-manager: 4sec.) So update
this link down period to 10 sec to properly trigger DHCP renew.

I probably don't follow: why do we need sucha a delay? If (with real
hardware) you plug network cable out and in one second you plug it in
you'll get DHCP renewed, right?

When I introduced RNDIS_STATUS_NETWORK_CHANGE handling by
emulating a
pair of up/down events I put 2 second delay to make link_watch happy

(as

quoted

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we only handle 1 event per second there) but 10 seconds sounds to much
to me.

In the test on Hyper-V, our software on host side  wants to trigger DHCP
renew by sending only a RNDIS_STATUS_NETWORK_CHANGE message to
a guest without physically unplug the cable. But, this message didn't trigger
DHCP renew within 2 seconds. The VM is Centos 7.1 using

Networkmanager,

quoted

which needs 4 seconds after link down to renew IP. Some daemon, like
ifplugd, needs 5 sec to renew. That's why we increase the simulated link
down time for RNDIS_STATUS_NETWORK_CHANGE message.

Yes, I understand the motivation but sorry if I was unclear with my
question. I meant to say that with physical network adapters it's
possible to trigger same two events by plugging your cable out and then
plugging it back in and it is certailnly doable in less than 10
seconds. NetworkManager or whoever is supposed to handle these events
and we don't really care how fast -- I think that 4 or 5 seconds
mentioned above is just an observation.

(forgot mailing lists in my last reply.... re-sending...)

Our test failed (i.e. not triggering DHCP renew) with existing 2sec delay. According 
to the ifplugd man page, it ignores link down time <5sec:
  http://linux.die.net/man/8/ifplugd
    -d | --delay-down= SECS Specify delay for deconfiguring interface (default: 5)

Networkmanager also has a waiting period (4sec).

Thanks,
- Haiyang