On Mon, 22 Jan 2024 12:16:27 +0800, Jason Wang <jasow...@redhat.com> wrote: > On Mon, Jan 22, 2024 at 12:00 PM Xuan Zhuo <xuanz...@linux.alibaba.com> wrote: > > > > On Mon, 22 Jan 2024 11:14:30 +0800, Jason Wang <jasow...@redhat.com> wrote: > > > On Mon, Jan 22, 2024 at 10:12 AM Zhu Yanjun <yanjun....@linux.dev> wrote: > > > > > > > > > > > > 在 2024/1/20 1:29, Andrew Lunn 写道: > > > > >>>>> while (!virtqueue_get_buf(vi->cvq, &tmp) && > > > > >>>>> - !virtqueue_is_broken(vi->cvq)) > > > > >>>>> + !virtqueue_is_broken(vi->cvq)) { > > > > >>>>> + if (timeout) > > > > >>>>> + timeout--; > > > > >>>> This is not really a timeout, just a loop counter. 200 iterations > > > > >>>> could > > > > >>>> be a very short time on reasonable H/W. I guess this avoid the soft > > > > >>>> lockup, but possibly (likely?) breaks the functionality when we > > > > >>>> need to > > > > >>>> loop for some non negligible time. > > > > >>>> > > > > >>>> I fear we need a more complex solution, as mentioned by Micheal in > > > > >>>> the > > > > >>>> thread you quoted. > > > > >>> Got it. I also look forward to the more complex solution to this > > > > >>> problem. > > > > >> Can we add a device capability (new feature bit) such as > > > > >> ctrq_wait_timeout > > > > >> to get a reasonable timeout? > > > > > The usual solution to this is include/linux/iopoll.h. If you can sleep > > > > > read_poll_timeout() otherwise read_poll_timeout_atomic(). > > > > > > > > I read carefully the functions read_poll_timeout() and > > > > read_poll_timeout_atomic(). The timeout is set by the caller of the 2 > > > > functions. > > > > > > FYI, in order to avoid a swtich of atomic or not, we need convert rx > > > mode setting to workqueue first: > > > > > > https://www.mail-archive.com/virtualization@lists.linux-foundation.org/msg60298.html > > > > > > > > > > > As such, can we add a module parameter to customize this timeout value > > > > by the user? > > > > > > Who is the "user" here, or how can the "user" know the value? > > > > > > > > > > > Or this timeout value is stored in device register, virtio_net driver > > > > will read this timeout value at initialization? > > > > > > See another thread. The design needs to be general, or you can post a RFC. > > > > > > In another thought, we've already had a tx watchdog, maybe we can have > > > something similar to cvq and use timeout + reset in that case. > > > > But we may block by the reset ^_^ if the device is broken? > > I mean vq reset here.
I see. I mean when the deivce is broken, the vq reset also many be blocked. void vp_modern_set_queue_reset(struct virtio_pci_modern_device *mdev, u16 index) { struct virtio_pci_modern_common_cfg __iomem *cfg; cfg = (struct virtio_pci_modern_common_cfg __iomem *)mdev->common; vp_iowrite16(index, &cfg->cfg.queue_select); vp_iowrite16(1, &cfg->queue_reset); while (vp_ioread16(&cfg->queue_reset)) msleep(1); while (vp_ioread16(&cfg->cfg.queue_enable)) msleep(1); } EXPORT_SYMBOL_GPL(vp_modern_set_queue_reset); In this function, for the broken device, we can not expect something. > > It looks like we have multiple goals here > > 1) avoid lockups, using workqueue + cond_resched() seems to be > sufficient, it has issue but nothing new > 2) recover from the unresponsive device, the issue for timeout is that > it needs to deal with false positives I agree. But I want to add a new goal, cvq async. In the netdim, we will send many requests via the cvq, so the cvq async will be nice. Thanks. > > Thanks > > > > > Thanks. > > > > > > > > > > Thans > > > > > > > > > > > Zhu Yanjun > > > > > > > > > > > > > > Andrew > > > > > > > > > >