Giant-free polling [PATCH]

[John Baldwin]

On Friday 11 March 2005 09:28 am, Gleb Smirnoff wrote:
> On Fri, Mar 11, 2005 at 03:14:50PM +0100, Pawel Jakub Dawidek wrote:
> P> On Fri, Mar 11, 2005 at 04:55:25PM +0300, dima wrote:
> P> +> I thought about using list also, but considered it to bring
> P> +> too much overhead to the code. The original idea of handling arrays
> P> +> seems to be very elegant.
> P>
> P> Overhead? Did you run any benchmarks to prove it?
> P> I find list-version much more elegant that using an array.
>
> It is also a small cookie for future. Now we have IFF_POLLING flag and
> IFCAP_POLLING, which indicate whether interface support polling and whether
> it actually does polling. This is not nice, from my viewpoint. I'd like
> to see only IFCAP_POLLING present and turning polling on/off for particular
> interface should be done by inserting/removing iface from polling list.
>
> This will also remove an extra unlocked check of interface flags (?).
>
> P> I also don't like the idea of calling handler method with two locks
> P> held (one sx and one mutex)...
>
> I agree with Pawel. We have LOR here between sx lock and driver lock:
>
> 	normal polling:	(get sx shared) -> (get driver mutex)
> 	driver stop:	(get driver mutex) -> (get sx exclusive)

You can't ever lock an sx(9) lock while holding a mutex.  FYI.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org