Re: netfront/netback multiqueue exhausting grants

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2016-01-20 at 15:16 +0000, Ian Campbell wrote:
> On Wed, 2016-01-20 at 10:10 -0500, Boris Ostrovsky wrote:
> > On 01/20/2016 10:02 AM, David Vrabel wrote:
> > > On 20/01/16 14:52, Ian Campbell wrote:
> > > > On Wed, 2016-01-20 at 09:40 -0500, Boris Ostrovsky wrote:
> > > > > On 01/20/2016 07:23 AM, Ian Campbell wrote:
> > > > > > There have been a few reports recently[0] which relate to a
> > > > > > failure of
> > > > > > netfront to allocate sufficient grant refs for all the queues:
> > > > > > 
> > > > > > [    0.533589] xen_netfront: can't alloc rx grant refs
> > > > > > [    0.533612] net eth0: only created 31 queues
> > > > > > 
> > > > > > Which can be worked around by increasing the number of grants
> > > > > > on
> > > > > > the
> > > > > > hypervisor command line or by limiting the number of queues
> > > > > > permitted
> > > > > > by
> > > > > > either back or front using a module param (which was broken but
> > > > > > is now
> > > > > > fixed on both sides, but I'm not sure it has been backported
> > > > > > everywhere
> > > > > > such that it is a reliable thing to always tell users as a
> > > > > > workaround).
> > > > > > 
> > > > > > Is there any plan to do anything about the default/out of the
> > > > > > box
> > > > > > experience? Either limiting the number of queues or making both
> > > > > > ends
> > > > > > cope
> > > > > > more gracefully with failure to create some queues (or both)
> > > > > > might be
> > > > > > sufficient?
> > > > > > 
> > > > > > I think the crash after the above in the first link at [0] is
> > > > > > fixed? I
> > > > > > think that was the purpose of ca88ea1247df "xen-netfront:
> > > > > > update
> > > > > > num_queues
> > > > > > to real created" which was in 4.3.
> > > > > I think ca88ea1247df is the solution --- it will limit the number
> > > > > of
> > > > > queues.
> > > > That's in 4.4, which the first link at [0] claimed to have tested.
> > > > I
> > > > can
> > > > see this fixing the crash, but does it really fix the "actually
> > > > works
> > > > with
> > > > less queues than it tried to get" issue?
> > 
> > That's what I thought it does too. I didn't notice that 4.4 was tested 
> > as well, so maybe not.
> 
> I've asked the reporter to send logs for the 4.4 case to xen-devel.

User confirmed[0] that 4.4 is actually OK.

Did someone request stable backports yet, or shall I do so?

Ian.

[0] http://lists.xen.org/archives/html/xen-users/2016-01/msg00110.html

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