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Tsirkin" To: Jason Wang Subject: Re: [PATCH v4] virtio_net: suppress cpu stall when free_unused_bufs Message-ID: <20230508024433-mutt-send-email-mst@kernel.org> References: <1683167226-7012-1-git-send-email-wangwenliang.1995@bytedance.com> <20230507093328-mutt-send-email-mst@kernel.org> <2b5cf90a-efa8-52a7-9277-77722622c128@redhat.com> <20230508020717-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: xuanzhuo@linux.alibaba.com, willemdebruijn.kernel@gmail.com, Wenliang Wang , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, zhengqi.arch@bytedance.com, virtualization@lists.linux-foundation.org, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, davem@davemloft.net X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; 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Sun, 07 May 2023 23:47:13 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ4vYeuFr5Bz2rslLpzPqeYDEDuyU1V6E3rGgoS88aNCbpJ9YMyQlWE3PZrEOwea2SRvN6MNbQ== X-Received: by 2002:a1c:f704:0:b0:3f1:9526:22be with SMTP id v4-20020a1cf704000000b003f1952622bemr6095754wmh.23.1683528433143; Sun, 07 May 2023 23:47:13 -0700 (PDT) Received: from redhat.com ([31.187.78.15]) by smtp.gmail.com with ESMTPSA id 2-20020a05600c22c200b003f42328b5d9sm3729073wmg.39.2023.05.07.23.47.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 May 2023 23:47:12 -0700 (PDT) Date: Mon, 8 May 2023 02:47:06 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: Wenliang Wang , davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, zhengqi.arch@bytedance.com, willemdebruijn.kernel@gmail.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, xuanzhuo@linux.alibaba.com Subject: Re: [PATCH v4] virtio_net: suppress cpu stall when free_unused_bufs Message-ID: <20230508024433-mutt-send-email-mst@kernel.org> References: <1683167226-7012-1-git-send-email-wangwenliang.1995@bytedance.com> <20230507093328-mutt-send-email-mst@kernel.org> <2b5cf90a-efa8-52a7-9277-77722622c128@redhat.com> <20230508020717-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 08, 2023 at 02:13:42PM +0800, Jason Wang wrote: > On Mon, May 8, 2023 at 2:08 PM Michael S. Tsirkin wrote: > > > > On Mon, May 08, 2023 at 11:12:03AM +0800, Jason Wang wrote: > > > > > > 在 2023/5/7 21:34, Michael S. Tsirkin 写道: > > > > On Fri, May 05, 2023 at 11:28:25AM +0800, Jason Wang wrote: > > > > > On Thu, May 4, 2023 at 10:27 AM Wenliang Wang > > > > > wrote: > > > > > > For multi-queue and large ring-size use case, the following error > > > > > > occurred when free_unused_bufs: > > > > > > rcu: INFO: rcu_sched self-detected stall on CPU. > > > > > > > > > > > > Fixes: 986a4f4d452d ("virtio_net: multiqueue support") > > > > > > Signed-off-by: Wenliang Wang > > > > > > --- > > > > > > v2: > > > > > > -add need_resched check. > > > > > > -apply same logic to sq. > > > > > > v3: > > > > > > -use cond_resched instead. > > > > > > v4: > > > > > > -add fixes tag > > > > > > --- > > > > > > drivers/net/virtio_net.c | 2 ++ > > > > > > 1 file changed, 2 insertions(+) > > > > > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > > > index 8d8038538fc4..a12ae26db0e2 100644 > > > > > > --- a/drivers/net/virtio_net.c > > > > > > +++ b/drivers/net/virtio_net.c > > > > > > @@ -3560,12 +3560,14 @@ static void free_unused_bufs(struct virtnet_info *vi) > > > > > > struct virtqueue *vq = vi->sq[i].vq; > > > > > > while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) > > > > > > virtnet_sq_free_unused_buf(vq, buf); > > > > > > + cond_resched(); > > > > > Does this really address the case when the virtqueue is very large? > > > > > > > > > > Thanks > > > > > > > > it does in that a very large queue is still just 64k in size. > > > > we might however have 64k of these queues. > > > > > > > > > Ok, but we have other similar loops especially the refill, I think we may > > > need cond_resched() there as well. > > > > > > Thanks > > > > > > > Refill is already per vq isn't it? > > Not for the refill_work(). > > Thanks Good point, refill_work probably needs cond_resched, too. And I guess virtnet_open? > > > > > > > > > > > > > > } > > > > > > > > > > > > for (i = 0; i < vi->max_queue_pairs; i++) { > > > > > > struct virtqueue *vq = vi->rq[i].vq; > > > > > > while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) > > > > > > virtnet_rq_free_unused_buf(vq, buf); > > > > > > + cond_resched(); > > > > > > } > > > > > > } > > > > > > > > > > > > -- > > > > > > 2.20.1 > > > > > > > >