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Tsirkin" To: Jiri Pirko Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, virtualization@lists.linux.dev, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, dave.taht@gmail.com, kerneljasonxing@gmail.com, hengqi@linux.alibaba.com Subject: Re: [PATCH net-next v3] virtio_net: add support for Byte Queue Limits Message-ID: <20240619014938-mutt-send-email-mst@kernel.org> References: <20240618144456.1688998-1-jiri@resnulli.us> <20240618140326-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Jun 19, 2024 at 07:45:16AM +0200, Jiri Pirko wrote: > Tue, Jun 18, 2024 at 08:18:12PM CEST, mst@redhat.com wrote: > >This looks like a sensible way to do this. > >Yet something to improve: > > > > > >On Tue, Jun 18, 2024 at 04:44:56PM +0200, Jiri Pirko wrote: > >> From: Jiri Pirko > >> > > [...] > > > >> +static void __free_old_xmit(struct send_queue *sq, struct netdev_queue *txq, > >> + bool in_napi, struct virtnet_sq_free_stats *stats) > >> { > >> unsigned int len; > >> void *ptr; > >> > >> while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) { > >> - ++stats->packets; > >> - > >> if (!is_xdp_frame(ptr)) { > >> - struct sk_buff *skb = ptr; > >> + struct sk_buff *skb = ptr_to_skb(ptr); > >> > >> pr_debug("Sent skb %p\n", skb); > >> > >> - stats->bytes += skb->len; > >> + if (is_orphan_skb(ptr)) { > >> + stats->packets++; > >> + stats->bytes += skb->len; > >> + } else { > >> + stats->napi_packets++; > >> + stats->napi_bytes += skb->len; > >> + } > >> napi_consume_skb(skb, in_napi); > >> } else { > >> struct xdp_frame *frame = ptr_to_xdp(ptr); > >> > >> + stats->packets++; > >> stats->bytes += xdp_get_frame_len(frame); > >> xdp_return_frame(frame); > >> } > >> } > >> + netdev_tx_completed_queue(txq, stats->napi_packets, stats->napi_bytes); > > > >Are you sure it's right? You are completing larger and larger > >number of bytes and packets each time. > > Not sure I get you. __free_old_xmit() is always called with stats > zeroed. So this is just sum-up of one queue completion run. > I don't see how this could become "larger and larger number" as you > describe. Oh. Right of course. Worth a comment maybe? Just to make sure we remember not to call __free_old_xmit twice in a row without reinitializing stats. Or move the initialization into __free_old_xmit to make it self-contained .. WDYT? > > > > >For example as won't this eventually trigger this inside dql_completed: > > > > BUG_ON(count > num_queued - dql->num_completed); > > Nope, I don't see how we can hit it. Do not complete anything else > in addition to what was started in xmit(). Am I missing something? > > > > > >? > > > > > >If I am right the perf testing has to be redone with this fixed ... > > > > > >> } > >> > > [...]