From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH net-next] virtio_net: ethtool tx napi configuration Date: Fri, 14 Sep 2018 11:27:18 +0800 Message-ID: <6db3c755-a1dc-dcc9-e110-bfc38143e83d@redhat.com> References: <20180909224449.203593-1-willemdebruijn.kernel@gmail.com> <2fd8d46f-7466-e507-af31-c587693beb6e@gmail.com> <4a3d69be-8651-e36d-bc14-5a3f1f23d155@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: f.fainelli@gmail.com, Network Development , David Miller , caleb.raitto@gmail.com, "Michael S. Tsirkin" , "Jon Olson (Google Drive)" , Willem de Bruijn To: Willem de Bruijn Return-path: Received: from mx1.redhat.com ([209.132.183.28]:37646 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728324AbeINIjy (ORCPT ); Fri, 14 Sep 2018 04:39:54 -0400 In-Reply-To: Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 2018年09月13日 22:58, Willem de Bruijn wrote: > On Thu, Sep 13, 2018 at 5:02 AM Jason Wang wrote: >> >> >> On 2018年09月13日 07:27, Willem de Bruijn wrote: >>> On Wed, Sep 12, 2018 at 3:11 PM Willem de Bruijn >>> wrote: >>>> On Wed, Sep 12, 2018 at 2:16 PM Florian Fainelli wrote: >>>>> >>>>> On 9/12/2018 11:07 AM, Willem de Bruijn wrote: >>>>>> On Wed, Sep 12, 2018 at 1:42 PM Florian Fainelli wrote: >>>>>>> >>>>>>> On 9/9/2018 3:44 PM, Willem de Bruijn wrote: >>>>>>>> From: Willem de Bruijn >>>>>>>> >>>>>>>> Implement ethtool .set_coalesce (-C) and .get_coalesce (-c) handlers. >>>>>>>> Interrupt moderation is currently not supported, so these accept and >>>>>>>> display the default settings of 0 usec and 1 frame. >>>>>>>> >>>>>>>> Toggle tx napi through a bit in tx-frames. So as to not interfere >>>>>>>> with possible future interrupt moderation, use bit 10, well outside >>>>>>>> the reasonable range of real interrupt moderation values. >>>>>>>> >>>>>>>> Changes are not atomic. The tx IRQ, napi BH and transmit path must >>>>>>>> be quiesced when switching modes. Only allow changing this setting >>>>>>>> when the device is down. >>>>>>> Humm, would not a private ethtool flag to switch TX NAPI on/off be more >>>>>>> appropriate rather than use the coalescing configuration API here? >>>>>> What do you mean by private ethtool flag? A new field in ethtool >>>>>> --features (-k)? >>>>> I meant using ethtool_drvinfo::n_priv_flags, ETH_SS_PRIV_FLAGS and then >>>>> ETHTOOL_GFPFLAGS and ETHTOOL_SPFLAGS to control the toggling of that >>>>> private flag. mlx5 has a number of privates flags for instance. >>>> Interesting, thanks! I was not at all aware of those ethtool flags. >>>> Am having a look. It definitely looks promising. >>> Okay, I made that change. That is indeed much cleaner, thanks. >>> Let me send the patch, initially as RFC. >>> >>> I've observed one issue where if we toggle the flag before bringing >>> up the device, it hits a kernel BUG at include/linux/netdevice.h:515 >>> >>> BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state)); >> This reminds me that we need to check netif_running() before trying to >> enable and disable tx napi in ethtool_set_coalesce(). > The first iteration of my patch checked IFF_UP and effectively > only allowed the change when not running. What do you mean > by need to check? I mean if device is not up, there's no need to toggle napi state and tx lock. > > And to respond to the other follow-up notes at once: > >> Consider we may have interrupt moderation in the future, I tend to use >> set_coalesce. Otherwise we may need two steps to enable moderation: >> >> - tx-napi on >> - set_coalesce > FWIW, I don't care strongly whether we do this through coalesce or priv_flags. Ok. >>> + if (!napi_weight) >>> + virtqueue_enable_cb(vi->sq[i].vq); >> I don't get why we need to disable enable cb here. > To avoid entering no-napi mode with too few descriptors to > make progress and no way to get out of that state. This is a > pretty crude attempt at handling that, admittedly. But in this case, we will call enable_cb_delayed() and we will finally get a interrupt? Thanks