On Tue, Dec 27, 2022 at 05:12:58PM +0800, Jason Wang wrote: > > 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. Poll just a bit :) Seriously I don't know, but at least check once after kick. > > > 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 BTW BAD_RING on removal will trigger dev_err. Not sure that is a good idea - can cause crashes if kernel panics on error. > > > > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
