On Tue, Jun 12, 2018 at 06:28:18PM +0200, Andrew Lunn wrote:
> On Mon, Jun 11, 2018 at 05:21:05PM +0530, Tejaswi Tanikella wrote:
> > On receiving a IGMPv2/v3 query, based on max_delay set in the header a
> > timer is started to send out a response after a random time within
> > max_delay. If the system then moves into suspend state, Report is
> > delayed until system wakes up.
> >
> > Use a alarmtimer instead of using a timer. Alarmtimer will wake the
> > system up from suspend to send out the IGMP report.
>
> Hi Tejaswi
>
> I think i must be missing something here. If we are suspended, we are
> not receiving multicast frames. If we are not receiving frames, why do
> we need to reply to the query?
>
> Once we resume, i expect we will reply to the next query. You could
> optimise restarting the flow by immediately sending a membership
> report, same as when the setsockopt is used to join the group.
>
> Andrew
Hi Andrew,
I'll try to explain my scenario. This was observed on a arm64 device.
An application registers for a mcast group, and just listens to mcast
packets. The connection is setup and mcast packets are being forwarded
by the router. Multicast packets are sent out every few minutes.
Not a very busy connection.
After some time the router sends out a IGMPv2 query. The max delay in
the header is set to 10s. The system starts a timer to send out the
response at 9s. But the device suspends and wakes up after 60s.
The response is sent out 50s late.
ftrace logs with boottime trace_clock and my igmp_logs:
4740693 kworker/0:3-395 [000] ..s2 4716.425695: igmp_log:
skbaddr=ffffffc156fe6600 daddr=224.0.0.1, id=0, rc=4295217721
4740694 kworker/0:3-395 [000] d.s4 4716.425717:
timer_start:timer=ffffffc217763140 function=igmp_timer_expire
expires=4295218678 [timeout=957] flags=0x00000000
timer set for 9.57 seconds. 957 jiffies
< device suspends >
< wakes up after ~60s >
4781289 <idle>-0 [000] .ns2 4779.170886: timer_expire_entry:
timer=ffffffc217763140 function=igmp_timer_expire now=4295218678
4781290 <idle>-0 [000] .ns2 4779.171045: igmp_log:
skbaddr=ffffffc1559d0e00 daddr=227.226.228.225, id=0, rc=4295218678
Since the response was delayed, mcast packets are not forwarded by the
router.
My changes use a alarmtimer, this will wake the system up if the timer
expires.
Thanks,
Tejaswi
