lkml.org 
[lkml]   [2022]   [Dec]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 3/4] virtio_ring: introduce a per virtqueue waitqueue
From

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


>
>

\
 
 \ /
  Last update: 2023-03-26 23:21    [W:0.079 / U:1.188 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site