Messages in this thread | | | Date | Tue, 27 Dec 2022 17:12:58 +0800 | Subject | Re: [PATCH 3/4] virtio_ring: introduce a per virtqueue waitqueue | From | Jason Wang <> |
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在 2022/12/27 15:33, Michael S. Tsirkin 写道: > On Tue, Dec 27, 2022 at 12:30:35PM +0800, Jason Wang wrote: >>> But device is still going and will later use the buffers. >>> >>> Same for timeout really. >> Avoiding infinite wait/poll is one of the goals, another is to sleep. >> If we think the timeout is hard, we can start from the wait. >> >> Thanks > If the goal is to avoid disrupting traffic while CVQ is in use, > that sounds more reasonable. E.g. someone is turning on promisc, > a spike in CPU usage might be unwelcome.
Yes, this would be more obvious is UP is used.
> > things we should be careful to address then: > 1- debugging. Currently it's easy to see a warning if CPU is stuck > in a loop for a while, and we also get a backtrace. > E.g. with this - how do we know who has the RTNL? > We need to integrate with kernel/watchdog.c for good results > and to make sure policy is consistent.
That's fine, will consider this.
> 2- overhead. In a very common scenario when device is in hypervisor, > programming timers etc has a very high overhead, at bootup > lots of CVQ commands are run and slowing boot down is not nice. > let's poll for a bit before waiting?
Then we go back to the question of choosing a good timeout for poll. And poll seems problematic in the case of UP, scheduler might not have the chance to run.
> 3- suprise removal. need to wake up thread in some way. what about > other cases of device breakage - is there a chance this > introduces new bugs around that? at least enumerate them please.
The current code did:
1) check for vq->broken 2) wakeup during BAD_RING()
So we won't end up with a never woke up process which should be fine.
Thanks
> >
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