On Thu, Sep 01, 2005 at 02:09:19PM -0400, Alan Stern wrote:
> Patrick and Greg:
>
> To put it baldly: Should klists be replaced with regular lists, each
> protected by an rwsem (or even a mutex)?
>
> The advantage of klists is that threads can remove or add nodes while
> other threads iterate through the list. With an rwsem, only one thread
> would be able to add or remove a node at a time, and only when no other
> thread was using the list. Considering that klists are currently used
> to hold:
>
> the set of all devices on a bus,
>
> the set of all drivers for a bus, and
>
> the set of all children of a device,
>
> (not counting the set of all devices bound to a driver, since
> there's already a patch to replace that with a mutex-protected
> regular list)
>
> this limitation on adding or removing doesn't seem significant. There
> aren't many places where these lists are iterated over or altered. We
> could remove most of the overhead associated with klists and get rid of an
> extra API for people to learn.
>
> Note that this would be very different from the old bus subsystem rwsem.
> That protected too much -- everything associated with the bus subsystem --
> making it a pronounced chokepoint. My suggestion involves a separate
> rwsem for each of these lists, so that none of them would be subject to
> much contention.
Might also be worth to do a micro-benchmark for it (maybe in userland).
The current klist code is far too complex for it's own good.
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