Re: [Xen-devel] [BUG] VIF rate limiting locks up network in the whole system

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-05-09 at 13:44 +0200, Jacek Konieczny wrote:

> No change in the 'rate' value here,

OK, that rules that out. Good.

>  but the 'features' are different.

Indeed.  Looks like gso-tcpv6, ipv6-csum-offload and split event
channels are new.

ipv6 seems unlikely to be related to your issues, since you look to be
using v4.

split-event-channels, could be I suppose be involved somehow.

[..]
> I have booted the Xen 4.4.0 host with an older kernel: 3.7.10

> The system does not lock up any more.

OK, so I think that makes it pretty certainly a kernel issue.

> 
> Xenstore variables for the backend:
> 
> /local/domain/1/device/vif/0/backend = "/local/domain/0/backend/vif/1/0"
>   (n1,r0)
> /local/domain/1/device/vif/0/backend-id = "0"   (n1,r0)
> /local/domain/1/device/vif/0/state = "4"   (n1,r0)
> /local/domain/1/device/vif/0/handle = "0"   (n1,r0)
> /local/domain/1/device/vif/0/mac = "02:00:0f:ff:00:1f"   (n1,r0)
> /local/domain/1/device/vif/0/tx-ring-ref = "9"   (n1,r0)
> /local/domain/1/device/vif/0/rx-ring-ref = "768"   (n1,r0)
> /local/domain/1/device/vif/0/event-channel = "11"   (n1,r0)
> /local/domain/1/device/vif/0/request-rx-copy = "1"   (n1,r0)
> /local/domain/1/device/vif/0/feature-rx-notify = "1"   (n1,r0)
> /local/domain/1/device/vif/0/feature-sg = "1"   (n1,r0)
> /local/domain/1/device/vif/0/feature-gso-tcpv4 = "1"   (n1,r0)
> /local/domain/1/device/vif/0/feature-gso-tcpv6 = "1"   (n1,r0)
> /local/domain/1/device/vif/0/feature-ipv6-csum-offload = "1"   (n1,r0)

Interestingly a different set of features to the 3.7.2 case. I am
guessing that the guest kernel differs on this other system, likely not
worth pursuing that.

> Is it possible, that one of the features introduced by the 3.13 kernel is
> faulty (e.g. the 'feature-split-event-channels')?

The guilty change may or may not be related to the new features, but it
could be.

> Is there a way to selectively enable/disable those features without changing
> the kernel?

Unfortunately I don't think so.

It *might* be possible to start the guest paused and then mess with the
feature advertisements in the backend's xenstore directory. Or that
might cause things to explode ;-). It's worth trying -- I think it will
be obvious if it hasn't worked, rather than being a subtle issue which
invalidate the testing...

> I will also try the 3.14.3 kernel, but I need to prepare it first.

Sounds good. Is there any chance you could bisect the releases between
3.7 and 3.14 to narrow down the range? I'd probably test the actual v3.X
tags/releases rather than using git bisect at this stage.

Ian.


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