From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: netfront/netback multiqueue exhausting grants Date: Thu, 21 Jan 2016 10:56:23 +0000 Message-ID: <56A0B957.9060101@citrix.com> References: <1453292623.26343.95.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1453292623.26343.95.camel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell , xen-devel Cc: Boris Ostrovsky , Wei Liu , David Vrabel List-Id: xen-devel@lists.xenproject.org On 20/01/16 12:23, 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 the correct solution is to increase the default maximum grant table size. Although, unless you're using the not-yet-applied per-cpu rwlock patches multiqueue is terrible on many (multisocket) systems and the number of queue should be limited in netback to 4 or even just 2. David