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Tsirkin" To: Maxime Coquelin Cc: Shannon Nelson , Jason Wang , xuanzhuo@linux.alibaba.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, davem@davemloft.net Subject: Re: [PATCH net-next v4 2/2] virtio-net: add cond_resched() to the command waiting loop Message-ID: <20230721110925-mutt-send-email-mst@kernel.org> References: <20230720083839.481487-1-jasowang@redhat.com> <20230720083839.481487-3-jasowang@redhat.com> <20230720170001-mutt-send-email-mst@kernel.org> <263a5ad7-1189-3be3-70de-c38a685bebe0@redhat.com> <20230721104445-mutt-send-email-mst@kernel.org> <6278a4aa-8901-b0e3-342f-5753a4bf32af@redhat.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6278a4aa-8901-b0e3-342f-5753a4bf32af@redhat.com> X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE, T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Fri, Jul 21, 2023 at 04:58:04PM +0200, Maxime Coquelin wrote: > > > On 7/21/23 16:45, Michael S. Tsirkin wrote: > > On Fri, Jul 21, 2023 at 04:37:00PM +0200, Maxime Coquelin wrote: > > > > > > > > > On 7/20/23 23:02, Michael S. Tsirkin wrote: > > > > On Thu, Jul 20, 2023 at 01:26:20PM -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 > > > > > > > > > > This still leaves hung processes, but at least it doesn't pin the CPU any > > > > > more. Thanks. > > > > > Reviewed-by: Shannon Nelson > > > > > > > > > > > > > I'd like to see a full solution > > > > 1- block until interrupt > > > > > > Would it make sense to also have a timeout? > > > And when timeout expires, set FAILED bit in device status? > > > > virtio spec does not set any limits on the timing of vq > > processing. > > Indeed, but I thought the driver could decide it is too long for it. > > The issue is we keep waiting with rtnl locked, it can quickly make the > system unusable. if this is a problem we should find a way not to keep rtnl locked indefinitely. > > > > 2- still handle surprise removal correctly by waking in that case > > > > > > > > > > > > > > > > > > --- > > > > > > 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(); > > > > > > + } > > > > > > > > > > > > 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 > > > > > >