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Re: [Xen-users] [Xen-devel] [BUG] 16 vcpus + 2 vif bridge = issue ?

i have already (by default) value of max_queues setted to 40 (system cores)
xcalc:/# more /sys/module/xen_netback/parameters/max_queues

domU netfront max_queues parameter has value equals to config vcpus paramater
test:~# more /sys/module/xen_netfront/parameters/max_queues

i've xen installed from git sources
and problem still exist

2015-09-25 13:45 GMT+03:00 Wei Liu <wei.liu2@xxxxxxxxxx>:
On Fri, Sep 25, 2015 at 10:49:39AM +0100, Ian Campbell wrote:
> On Fri, 2015-09-25 at 10:41 +0100, Ian Campbell wrote:
> > On Thu, 2015-09-24 at 23:49 +0300, Roman Shubovich wrote:
> > > here is my configs and log/tcpdump/ping/dmesg output
> > > i see no visible changes in all of the logs output, but 16vcpus domU
> > > didn't work properly
> > >
> > >
> > > and one more thing:
> > > when i try to start domU with vcpus more than 16 then domU won't start
> > > at
> > > all
> >
> > This looks similar to an issue report on xen-users earlier in the week.
> > Please check the list archives for the thread "Xen bridging issue", IIRC
> > patches were proposed but I'm not sure what the status of those is.
> Comparing your logs it looks like this was the issue with <=16 VCPUS too:
> $ diff -u <(sed -e 's/^\[.....\.......\]\s*//g' A) <(sed -e 's/^\[.....\.......\]\s*//g' B)
> [...]
> @@ -249,6 +252,8 @@
>Â i8042: PNP: No PS/2 controller found. Probing ports directly.
>Â blkfront: xvda: barrier or flush: disabled; persistent grants: enabled; indirect descriptors: enabled;
>Â xvda: unknown partition table
> +xen_netfront: can't alloc rx grant refs
> +net eth1: only created 15 queues

This is multiqueue exhausting grant table references.

You're supposed to be able to set a netback parameter to control default
number of maximum queues get created. Unfortunately there is a bug in
the code which renders the setting of that parameter when loading
netback useless.

A workaround is to

1. Insert netback in Dom0.
2. echo $NR_MAX_QUEUES_YOU_WANT > /sys/module/xen_netback/parameters/max_queues
3. Start guest.

Alternatively you can set max_queues parameter of netfront in guest.
However that's also affected by similar bug...

Patches to both netback and netfront were merged some time ago. I'm not
sure when they will trickle down to your distro.


>Â i8042: No controller found
>Â mousedev: PS/2 mouse device common for all mice
>Â rtc_cmos rtc_cmos: rtc core: registered rtc_cmos as rtc0
> It's just a bit less noisy about it in this case for some reason.
> Ian.

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