From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Fastabend Subject: Re: [RFC PATCH] virtio_net: XDP support for adjust_head Date: Thu, 5 Jan 2017 19:28:23 -0800 Message-ID: <586F0ED7.7060508@gmail.com> References: <20170102194413.9089.39078.stgit@john-Precision-Tower-5810> <73715f7a-eeeb-679f-a7b8-7b1fefe1757e@redhat.com> <20170104001332-mutt-send-email-mst@kernel.org> <586ECF53.1070700@gmail.com> <20170106023825-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: Jason Wang , john.r.fastabend@intel.com, netdev@vger.kernel.org, alexei.starovoitov@gmail.com, daniel@iogearbox.net To: "Michael S. Tsirkin" Return-path: Received: from mail-pg0-f66.google.com ([74.125.83.66]:32959 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752858AbdAFD2f (ORCPT ); Thu, 5 Jan 2017 22:28:35 -0500 Received: by mail-pg0-f66.google.com with SMTP id g1so42594845pgn.0 for ; Thu, 05 Jan 2017 19:28:35 -0800 (PST) In-Reply-To: <20170106023825-mutt-send-email-mst@kernel.org> Sender: netdev-owner@vger.kernel.org List-ID: On 17-01-05 04:39 PM, Michael S. Tsirkin wrote: > On Thu, Jan 05, 2017 at 02:57:23PM -0800, John Fastabend wrote: >> On 17-01-03 02:16 PM, Michael S. Tsirkin wrote: >>> On Tue, Jan 03, 2017 at 02:01:27PM +0800, Jason Wang wrote: >>>> >>>> >>>> On 2017年01月03日 03:44, John Fastabend wrote: >>>>> Add support for XDP adjust head by allocating a 256B header region >>>>> that XDP programs can grow into. This is only enabled when a XDP >>>>> program is loaded. >>>>> >>>>> In order to ensure that we do not have to unwind queue headroom push >>>>> queue setup below bpf_prog_add. It reads better to do a prog ref >>>>> unwind vs another queue setup call. >>>>> >>>>> : There is a problem with this patch as is. When xdp prog is loaded >>>>> the old buffers without the 256B headers need to be flushed so that >>>>> the bpf prog has the necessary headroom. This patch does this by >>>>> calling the virtqueue_detach_unused_buf() and followed by the >>>>> virtnet_set_queues() call to reinitialize the buffers. However I >>>>> don't believe this is safe per comment in virtio_ring this API >>>>> is not valid on an active queue and the only thing we have done >>>>> here is napi_disable/napi_enable wrappers which doesn't do anything >>>>> to the emulation layer. >>>>> >>>>> So the RFC is really to find the best solution to this problem. >>>>> A couple things come to mind, (a) always allocate the necessary >>>>> headroom but this is a bit of a waste (b) add some bit somewhere >>>>> to check if the buffer has headroom but this would mean XDP programs >>>>> would be broke for a cycle through the ring, (c) figure out how >>>>> to deactivate a queue, free the buffers and finally reallocate. >>>>> I think (c) is the best choice for now but I'm not seeing the >>>>> API to do this so virtio/qemu experts anyone know off-hand >>>>> how to make this work? I started looking into the PCI callbacks >>>>> reset() and virtio_device_ready() or possibly hitting the right >>>>> set of bits with vp_set_status() but my first attempt just hung >>>>> the device. >>>> >>>> Hi John: >>>> >>>> AFAIK, disabling a specific queue was supported only by virtio 1.0 through >>>> queue_enable field in pci common cfg. >>> >>> In fact 1.0 only allows enabling queues selectively. >>> We can add disabling by a spec enhancement but >>> for now reset is the only way. >>> >>> >>>> But unfortunately, qemu does not >>>> emulate this at all and legacy device does not even support this. So the >>>> safe way is probably reset the device and redo the initialization here. >>> >>> You will also have to re-apply rx filtering if you do this. >>> Probably sending notification uplink. >>> >> >> The following seems to hang the device on the next virtnet_send_command() >> I expected this to meet the reset requirements from the spec because I >> believe its the same flow coming out of restore(). For a real patch we >> don't actually need to kfree all the structs and reallocate them but >> I was expecting the below to work. Any ideas/hints? > > Restore assumes device was previously reset. > You want to combine freeze+restore. Yep the below is actually freeze+restore I just omitted the freeze portion from the description. > >> static int virtnet_xdp_reset(struct virtnet_info *vi) >> { >> int i, ret; >> // insert flush_work here doesn't seem to help hang. >> netif_device_detach(vi->dev); >> cancel_delayed_work_sync(&vi->refill); >> if (netif_running(vi->dev)) { >> for (i = 0; i < vi->max_queue_pairs; i++) >> napi_disable(&vi->rq[i].napi); >> } >> >> remove_vq_common(vi, false); // everything above is freeze sans flush_work and virtnet_cpu_notif_remove // the rest below is restore where I call virtnet_set_queues later outside // the reset function. >> ret = init_vqs(vi); >> if (ret) >> return ret; >> virtio_device_ready(vi->vdev); >> >> if (netif_running(vi->dev)) { >> for (i = 0; i < vi->curr_queue_pairs; i++) >> if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL)) >> schedule_delayed_work(&vi->refill, 0); >> >> for (i = 0; i < vi->max_queue_pairs; i++) >> virtnet_napi_enable(&vi->rq[i]); >> } >> netif_device_attach(vi->dev); >> return 0; >> } Could be a locking problem I'm missing so I'll look at it a bit more but good to know we expect freeze/restore to reset the device. .John