Re: [Xen-devel] netfront/netback multiqueue exhausting grants

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

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.
-boris

> > In any case having exhausted the grant entries creating queues there aren't
> > any left to shuffle actual data around, is there? (or are those
> > preallocated too?)
> All grants refs for Tx and Rx are preallocated (this is the allocation
> that is failing above).
>
> David

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel