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[80.230.48.7]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e7040a9a9sm225839165e9.9.2026.05.10.11.28.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 10 May 2026 11:28:02 -0700 (PDT) Date: Sun, 10 May 2026 14:27:59 -0400 From: "Michael S. Tsirkin" To: Simon Schippers Cc: willemdebruijn.kernel@gmail.com, jasowang@redhat.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, eperezma@redhat.com, leiyang@redhat.com, stephen@networkplumber.org, jon@nutanix.com, tim.gebauer@tu-dortmund.de, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux.dev Subject: Re: [PATCH net-next v11 1/4] tun/tap: add ptr_ring consume helper with netdev queue wakeup Message-ID: <20260510142743-mutt-send-email-mst@kernel.org> References: <20260508151048.183125-1-simon.schippers@tu-dortmund.de> <20260508151048.183125-2-simon.schippers@tu-dortmund.de> <20260509183518-mutt-send-email-mst@kernel.org> <9a4458fc-61f2-469b-8260-f144d3827b5d@tu-dortmund.de> <20260510094020-mutt-send-email-mst@kernel.org> <20260510114401-mutt-send-email-mst@kernel.org> <5f39493e-b2f0-446b-9896-98a074f5ed6b@tu-dortmund.de> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <5f39493e-b2f0-446b-9896-98a074f5ed6b@tu-dortmund.de> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 3CDPK0zFHFEakEOgLqlNe4M0R91s9jM-WUGqfKRdW2k_1778437684 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Sun, May 10, 2026 at 06:22:15PM +0200, Simon Schippers wrote: > On 5/10/26 17:44, Michael S. Tsirkin wrote: > > On Sun, May 10, 2026 at 04:01:39PM +0200, Simon Schippers wrote: > >> On 5/10/26 15:40, Michael S. Tsirkin wrote: > >>> On Sun, May 10, 2026 at 10:55:34AM +0200, Simon Schippers wrote: > >>>> On 5/10/26 09:03, Simon Schippers wrote: > >>>>> On 5/10/26 00:44, Michael S. Tsirkin wrote: > >>>>>> On Sat, May 09, 2026 at 06:31:47PM +0200, Simon Schippers wrote: > >>>>>>> On 5/8/26 17:10, Simon Schippers wrote: > >>>>>>>> +static void tun_queue_purge(struct tun_struct *tun, struct tun_file *tfile) > >>>>>>>> { > >>>>>>>> void *ptr; > >>>>>>>> > >>>>>>>> - while ((ptr = ptr_ring_consume(&tfile->tx_ring)) != NULL) > >>>>>>>> + while ((ptr = tun_ring_consume(tun, tfile)) != NULL) > >>>>>>>> tun_ptr_free(ptr); > >>>>>>>> > >>>>>>>> skb_queue_purge(&tfile->sk.sk_write_queue); > >>>>>>> > >>>>>>> Sashiko is right once again. tun_ring_consume() in tun_queue_purge() > >>>>>>> operates on a tfile that is being torn down. Its queue_index is no > >>>>>>> longer valid. After the swap in __tun_detach(), it points to the > >>>>>>> netdev subqueue of a different tfile. > >>>>>>> --> We should not wake there. > >>>>>> > >>>>>> Does it not exactly point at ntfile which is what we want to wake? > >>>>>> > >>>>> > >>>>> I see your point. But calling tun_ring_consume() as done here is > >>>>> wrong, because it does not wake if the tx_ring of the tfile > >>>>> (that is currently torn down) is empty. We could change > >>>>> tun_ring_consume() to call __tun_wake_queue() > >>>>> with consumed=0 if !ptr but I think this would slow down the consumer > >>>>> path. > >>>>> > >>>> > >>>> My statement is wrong: > >>>> There is no way that the tx_ring is empty and the queue is stopped > >>>> at the same time. So we do not need to touch tun_ring_consume() and > >>>> this works just fine. > >>>> > >>>>>> > >>>>>>> I will swap tun_ring_consume() with ptr_ring_consume() again and > >>>>>>> submit a v12 :) > >>>>>> > >>>>>> If so then maybe > >>>>>> netif_tx_wake_queue(netdev_get_tx_queue(tun->dev, index)); > >>>>>> > >>>>> > >>>>> But we should only do this if there is space in the ntfile. > >>>>> My approach: > >>>>> > >>>>> @@ -586,12 +588,18 @@ static void __tun_detach(struct tun_file *tfile, bool clean) > >>>>> BUG_ON(index >= tun->numqueues); > >>>>> > >>>>> rcu_assign_pointer(tun->tfiles[index], > >>>>> tun->tfiles[tun->numqueues - 1]); > >>>>> ntfile = rtnl_dereference(tun->tfiles[index]); > >>>>> + spin_lock(&ntfile->tx_ring.consumer_lock); > >>>>> ntfile->queue_index = index; > >>>>> ntfile->xdp_rxq.queue_index = index; > >>>>> + ntfile->cons_cnt = 0; > >>>>> + if (__ptr_ring_empty(&ntfile->tx_ring)) { > >>>>> + netif_wake_subqueue(tun->dev, index); > >>>>> + } > >>>>> + spin_unlock(&ntfile->tx_ring.consumer_lock); > >>>>> rcu_assign_pointer(tun->tfiles[tun->numqueues - 1], > >>>>> NULL); > >>>>> > >>>>> ntfile->cons_cnt is unvalid, because the new queue might not be stopped. > >>>>> That is the reason why I reset it to 0. > >>>> > >>>> However, I still prefer this approach because the code is easier to > >>>> understand. > >>> > >>> > >>> So do you want me to finish review of this one and ack, or want to > >>> post v12? > >>> > >> > >> I will post a v12 with the proposed changes for patch 1. > >> No other changes. > >> > >> Thanks! > > > > actually can you clarify? why only when ntfile ring is empty? > > > > This avoids waking when ntfile->tx_ring is full. We can not use > __ptr_ring_can_produce() with consumer locks, therefore I chose > __ptr_ring_empty() instead. > > If there are any elements in ntfile->tx_ring we do not have to wake. > This will be done by the consumer in tun_ring_consume() & > __tun_wake_queue() after consuming those elements. worth a code comment if you need to do v13.