From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [net PATCH v5 1/6] virtio_net: use dev_kfree_skb for small buffer XDP receive Date: Wed, 25 Jan 2017 16:45:25 +0200 Message-ID: <20170125163003-mutt-send-email-mst@kernel.org> References: <20170117221443.20280.62546.stgit@john-Precision-Tower-5810> <20170117221950.20280.39496.stgit@john-Precision-Tower-5810> <20170123230809-mutt-send-email-mst@kernel.org> <20170124.144328.2195698124358175034.davem@davemloft.net> <20170124215412-mutt-send-email-mst@kernel.org> <20170125051810-mutt-send-email-mst@kernel.org> <58882355.70307@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: Jason Wang , David Miller , john.r.fastabend@intel.com, netdev@vger.kernel.org, alexei.starovoitov@gmail.com, daniel@iogearbox.net To: John Fastabend Return-path: Received: from mx1.redhat.com ([209.132.183.28]:47016 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750748AbdAYOp0 (ORCPT ); Wed, 25 Jan 2017 09:45:26 -0500 Content-Disposition: inline In-Reply-To: <58882355.70307@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Jan 24, 2017 at 08:02:29PM -0800, John Fastabend wrote: > On 17-01-24 07:23 PM, Michael S. Tsirkin wrote: > > On Wed, Jan 25, 2017 at 10:57:12AM +0800, Jason Wang wrote: > >> > >> > >> On 2017年01月25日 04:08, Michael S. Tsirkin wrote: > >>> On Tue, Jan 24, 2017 at 02:43:28PM -0500, David Miller wrote: > >>>> From: "Michael S. Tsirkin" > >>>> Date: Mon, 23 Jan 2017 23:08:35 +0200 > >>>> > >>>>> On Tue, Jan 17, 2017 at 02:19:50PM -0800, John Fastabend wrote: > >>>>>> In the small buffer case during driver unload we currently use > >>>>>> put_page instead of dev_kfree_skb. Resolve this by adding a check > >>>>>> for virtnet mode when checking XDP queue type. Also name the > >>>>>> function so that the code reads correctly to match the additional > >>>>>> check. > >>>>>> > >>>>>> Fixes: bb91accf2733 ("virtio-net: XDP support for small buffers") > >>>>>> Signed-off-by: John Fastabend > >>>>>> Acked-by: Jason Wang > >>>>> Acked-by: Michael S. Tsirkin > >>>>> > >>>>> I think we definitely want this one in -net as it's > >>>>> a bugfix. > >>>> This whole series is a bug fix, we must have adjust_header XDP > >>>> support in the virtio_net driver before v4.10 goes out, it is > >>>> a requires base feature for XDP. > >>> I have to say device resets outside probe have a huge potential > >>> to uncover hypervisor bugs. > >> > >> Maybe not if it reuses most of current codes? Since we've already used them > >> in sleep or hibernation? > >> > >> Thanks > > > > Except almost no one uses sleep or hybernate with VMs. I'm not saying > > it's a bad idea, just that it needs a lot of testing before release and > > we won't get enough if we merge at this point. > > > > Then it would seem like a good thing to have another user of these paths and > find the bugs versus letting them sit there for some poor folks who do use > sleep/hybernate. Absolutely. But -rc6 is not the time to test waters IMO. > >>> I am rather uncomfortable > >>> doing that after -rc1. > >>> > >>> How about a module option to disable it by default? > >>> We can then ship a partial implementation in 4.10 > >>> and work on completing it in 4.11. > >>> > > Ugh I would prefer to avoid module options. This will only happen if users > push XDP program into driver anyways. Again I agree, it's an idea for a stopgap measure so we can have something in 4.10 - and also assuming that 256b headroom is a must. > > > > To clarify, I'm thinking an option similar to enable_xdp, > > and have all packets have a 256 byte headroom for 4.10. > > An option where? In QEMU side, in driver? Is the reset really that bad, coming > from a hardware driver side lots of configuration changes can cause resets. I > agree its not overly elegant but could follow on patches be used to make it > prettier if possible. Again I agree and it's not that bad it's just not something we should do past rc5. > I know folks prefer to avoid tuning knobs but I think exposing the headroom > configuration to users might not be a bad idea. After all these same users are > already programming maps and ebpf codes. A simple tuning knob should not be a > big deal and reasonable defaults would of course be used. That is a net-next > debate though. No arguments from my side here. > > > > Consider our options for 4.11. > > > > Finally just to point out here are the drivers with XDP support on latest > net tree, > > mlx/mlx5 > mlx/mlx4 > qlogic/qede > netronome/nfp > virtio_net > > And here is the list of adjust header support, > > mlx/mlx4 Above seems to imply an interface for userspace to detect the amount of head space would be benefitial. > > So we currently have the same feature gap on all the other drivers except one. > Although I do not think that is a very good excuse. Lets figure out what we > should do about virtio. > > Thanks, > John If we can simply defer adjust_head patches to 4.11 then that's fine. -- MST