On Mon, Jan 22, 2024 at 4:04 PM Xuan Zhuo <xuanz...@linux.alibaba.com> wrote:
>
> On Mon, 22 Jan 2024 15:57:08 +0800, Jason Wang <jasow...@redhat.com> wrote:
> > On Mon, Jan 22, 2024 at 3:36 PM Xuan Zhuo <xuanz...@linux.alibaba.com>
> > wrote:
> > >
> > > On Mon, 22 Jan 2024 15:19:12 +0800, Jason Wang <jasow...@redhat.com>
> > > wrote:
> > > > On Mon, Jan 22, 2024 at 3:07 PM Xuan Zhuo <xuanz...@linux.alibaba.com>
> > > > wrote:
> > > > >
> > > > > On Mon, 22 Jan 2024 14:58:09 +0800, Jason Wang <jasow...@redhat.com>
> > > > > wrote:
> > > > > > On Mon, Jan 22, 2024 at 2:55 PM Jason Wang <jasow...@redhat.com>
> > > > > > wrote:
> > > > > > >
> > > > > > > On Mon, Jan 22, 2024 at 2:20 PM Xuan Zhuo
> > > > > > > <xuanz...@linux.alibaba.com> wrote:
> > > > > > > >
> > > > > > > > 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.
> > > > > > >
> > > > > > > Yes, it's best effort, there's no guarantee then. But it doesn't
> > > > > > > harm to try.
> > > > > > >
> > > > > > > Thanks
> > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > >
> > > > > > > > > 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.
> > > > > >
> > > > > > Then you need an interrupt for cvq.
> > > > > >
> > > > > > FYI, I've posted a series that use interrupt for cvq in the past:
> > > > > >
> > > > > > https://lore.kernel.org/lkml/6026e801-6fda-fee9-a69b-d06a80368...@redhat.com/t/
> > > > >
> > > > > I know this. But the interrupt maybe not a good solution without new
> > > > > space.
> > > >
> > > > What do you mean by "new space"?
> > >
> > > Yes, I know, the cvq can work with interrupt by the virtio spec.
> > > But as I know, many hypervisors implement the cvq without supporting
> > > interrupt.
> >
> > It's a bug of the hypervisor that needs to be fix. Interrupt is
> > provided by transport not the virtio itself.
>
> YES. I agree.
>
> But I still think we should not work with interrupt without any negotiation
> directly. I more like to introduce a new feature to enable this.
I can hardly believe we need to workaround the issue of specific
hypervisors like this...
Thanks
>
> Thanks.
>
>
