Re: [patch 13/13] signal/timer/event fds v9 - KAIO eventfd supportexample ...

[Avi Kivity]

Davide Libenzi wrote:

 

> > I think it's a bit too fine grained, and a new system call (io_bindfd()?)
> > would be easier to use.  In addition, you would move the eventfd_fget() out of
> > the submission path.
> >     
>
> IMO the cost of the eventfd_fget() (have you seen it?) is not worth adding 
> a new syscall.
>   

There's an atomic op there (and another on the way out).  Probably on a 
busy cacheline.  Still it's probably lost in the noise.

Regardless of that, I think that specifying the fd per submission is 
wrong.  It feels like a setup thing that needs to be done once.  We 
shouldn't skimp on syscalls, especially on something as important as 
unifying the async event model.


> Actually, the flags field that Linus suggested may be given an extra meaning of 
> "bind to ctx", that'd solve the problem w/out new syscalls.
>
>   

I don't see how.  It's still per submission.  You could do it on the 
first iocb, but that's just adding warts to the API.

You could add an IO_CMD_BIND_EVENTFD, but that feels wrong too, as it 
isn't really an I/O command.


--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/