On Sun, Aug 31, 2014 at 01:40:35PM -0700, Greg KH wrote: > On Sun, Aug 31, 2014 at 01:14:07PM -0700, Dmitry Torokhov wrote: > > On Sun, Aug 31, 2014 at 12:31:40PM -0700, Greg KH wrote: > > > On Sun, Aug 31, 2014 at 12:24:46PM -0700, Arjan van de Ven wrote: > > > > >>before we added the current async approach the approach of async init > > > > >>calls was tried > > > > >>At the time, Linus hated it and he was right, it was not the right > > > > >>thing. > > > > >> > > > > >>What is different this time to make this the right thing to do ? > > > > > > > > > >Because otherwise drivers still have to do this, but open code it. > > > > >Let's say I > > > > >have a long operations (i.e. for some touchpads it takes about 2 secs > > > > >to reset > > > > >and configure it). I can offload that part into async_schedule() so it > > > > >does not > > > > >stop initialization of the rest of the system (why would I want to > > > > >delay > > > > >initializing of USB or storage system until touchpad is ready?) but if > > > > >that > > > > >initialization fails we end up with partially bound driver and device > > > > >that is > > > > >not really operable. I would very much prefer async and sync cases be > > > > >the same > > > > >- if probe() fails the driver is not bound to the device. > > > > > > > > > >I think it is wrong to make async probing system-wide, but driver > > > > >opt-in shoudl > > > > >be fine and right thing to do. > > > > > > > > > > > > > I am completely fine if we make basically an async wrapper for > > > > pci_register_driver() and friends.. that would be convenient I suppose. > > > > > > > > (but then again, in reality very few drivers take real time to init... > > > > most already > > > > do the heavy work in open(). Not all can, sure, but if you look at a > > > > bootgraph.pl > > > > graph of a typical boot it's only a few that matter). > > > > Input devices normally can't as we need to publish their capabilities before > > users start opening them. > > > > > > And many drivers need to register with a subsystem, and there's some > > > > ordering around that, > > > > and that's why we ended up with the async cookie stuff, so that you can > > > > do the > > > > heavy work in parallel, but order near the end at > > > > registeration-with-the-subsystem time. > > > > > > > > But doing this on an initcall level was wrong back then, and I have yet > > > > to hear > > > > a reason why it would be right this time. > > > > > > It's still wrong, it's not what I was thinking about when talking this > > > over with Luis and Dmitry, I think something got lost in the > > > translation... > > > > Right, all (well almost all) I wanted is for individual drivers to declare > > their probe() functions asynchronous and driver core scheduling async attach > > and properly handle failures from it. > > Yes, that's what I want as well. > > Luis, care to redo the patches in this way? It should be a lot simpler > (no messing around with init levels and linker fun...)
Sure, when we spoke the requirement was indeed clear but as I noted on the description on this cover letter as I reviewed Wu Zhangjin's RFC which used async_schedule() he ran into the issue of eventually grouping things. I went with this approach as a first shot given that we have a long tested set of groupings already done by the kernel so this tried to take advantage of that should we try to scale on asynchronous probing. I still believe its a good approach if we wanted to scale it but that would require the desire to do so, I obviously considered it worthwhile as I shaved off at least ~1 second off kernel boot time when doing an original proof of concept and only doing drivers, and taking into consideration my kenrel takes ~5 seconds before userspace is reached. I'll toss this in the bin for now though and send something based on Tejun's approach shortly! Luis -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
