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.
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
Thanks
>
> Thanks.
>
>
> >
> > Thans
> >
> > >
> > > Zhu Yanjun
> > >
> > > >
> > > > Andrew
> > >
> >
>
