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Tsirkin" To: Shannon Nelson Subject: Re: [PATCH net-next v4 2/2] virtio-net: add cond_resched() to the command waiting loop Message-ID: <20230720164930-mutt-send-email-mst@kernel.org> References: <20230720083839.481487-1-jasowang@redhat.com> <20230720083839.481487-3-jasowang@redhat.com> 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, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, edumazet@google.com, kuba@kernel.org, maxime.coquelin@redhat.com, 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; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Thu, Jul 20, 2023 at 08:31:13AM -0700, Shannon Nelson wrote: > On 7/20/23 1:38 AM, Jason Wang wrote: > > > > Adding cond_resched() to the command waiting loop for a better > > co-operation with the scheduler. This allows to give CPU a breath to > > run other task(workqueue) instead of busy looping when preemption is > > not allowed on a device whose CVQ might be slow. > > > > Signed-off-by: Jason Wang > > --- > > drivers/net/virtio_net.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index 9f3b1d6ac33d..e7533f29b219 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -2314,8 +2314,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd, > > * into the hypervisor, so the request should be handled immediately. > > */ > > while (!virtqueue_get_buf(vi->cvq, &tmp) && > > - !virtqueue_is_broken(vi->cvq)) > > + !virtqueue_is_broken(vi->cvq)) { > > + cond_resched(); > > cpu_relax(); > > + } > > The cover letter suggests that this addresses the infinite poll for buggy > devices, but I don't see how that is resolved here. This should make it a > little nicer to the system, but it still is going to poll forever on a > device that has gone catatonic. Is there a reason that I'm missing that we > don't have a polling limit here? > > sln we don't know what the limit would be. but given it's a workqueue now, why does it still have to poll as opposed to blocking? > > > > return vi->ctrl->status == VIRTIO_NET_OK; > > } > > -- > > 2.39.3 > > > > _______________________________________________ > > Virtualization mailing list > > Virtualization@lists.linux-foundation.org > > https://lists.linuxfoundation.org/mailman/listinfo/virtualization _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization