Re: [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifierinterface

[Davide Libenzi]

On Thu, 18 Jun 2009, Michael S. Tsirkin wrote:

> On Wed, Jun 17, 2009 at 04:21:19PM -0700, Davide Libenzi wrote:
> > The interface is just ugly IMO. You have eventfd_signal() that can sleep, 
> > or not, depending on the registered ->signal() function implementations.
> > This is pretty bad, a lot worse than the theoretical us spent in the 
> > schedule_work() processing.
> 
> I agree. How about the idea of introducing eventfd_signal_from_task
> which can sleep? Does this sound same?

You're basically asking to double the size of eventfd, make the signal 
path heavier, make the eventf size bigger, w/out having provided any *real 
life* measurement whatsoever to build a case for it.
WAY too much stuff went in by just branding the latest coolest names as 
reasons for them.
And all this to remove the wakeup of a *kernel* thread going to run in the 
same CPU where the work has been scheduled.
Come back with *replicable* real life benchmarks, and then we'll see what 
the best approach to address it will be.



- Davide


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