On Mon, Jul 22, 2019 at 11:14:39AM -0400, Joel Fernandes wrote:

[snip]

quoted

quoted

Would it make sense to have call_rcu() check to see if there are many
outstanding requests on this CPU and if so process them before returning?
That would ensure that frequent callers usually ended up doing their
own processing.

Other than what Paul already mentioned about deadlocks, I am not sure if this
would even work for all cases since call_rcu() has to wait for a grace
period.

So, if the number of outstanding requests are higher than a certain amount,
then you *still* have to wait for some RCU configurations for the grace
period duration and cannot just execute the callback in-line. Did I miss
something?

Can waiting in-line for a grace period duration be tolerated in the vhost case?

thanks,

 - Joel

No, but it has many other ways to recover (try again later, drop a
packet, use a slower copy to/from user).

-- 
MST

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