On Sunday, July 29, 2012, Rafael J. Wysocki wrote: > On Sunday, July 29, 2012, Alan Stern wrote: > > On Sun, 29 Jul 2012, Rafael J. Wysocki wrote: > > > > > The difference is, if you use _put_sync(), you need to wait the extra 10 ms > > > for local_pci_probe() to return (if the parent is actually suspended), > > > although you might not need to wait for it if you used _put(), right? > > > > Yes, that's the difference. But who waits for local_pci_probe() to > > return? :-) > > pci_register_driver() might, but that's not a big deal. Hot-plug might > as well, though. > > > > Which, to me, means that using _put_sync() may not be always better. > > > It probably doesn't matter a lot, but then the workqueue overhead shouldn't > > > matter a lot either. > > > > It's that in the end, the extra overhead is pretty small. For me > > there's also an issue of style: If you do a synchronous get then it > > looks odd not to do a synchronous put. My feeling has always been that > > the async routines are for use in non-process contexts, where the sync > > routines can't be used. Using them just to return a little more > > quickly is a foreign idea. > > I see. :-) > > The reason for using sync get is quite obvious: we want to be able to access > the device later on. For sync put that's not so clear, though. There are cases > when we definitely want to do it, like the failing .probe() in which we want to > disable runtime PM next to the put, but usually it doesn't hurt (too much) to > defer it IMO. Now it occured to me that perhaps we don't need the current asynchronous pm_runtime_get() at all. The usefulness of it is quite questionable, because either we want to resume the device immediately, for which pm_runtime_get_sync() should be used, or we just want to bump up the usage counter, in which cases pm_runtime_get_noresume() should always be sufficient. I fail to see any particularly compelling use case for pm_runtime_get() doing an asynchronous resume at the moment, but perhaps that's just me. However, I receive reports of people using pm_runtime_get() where they really should use pm_runtime_get_sync(), so I wonder if we can simply rename pm_runtime_get_sync() as pm_runtime_get() and drop the asynchronous version altogether? Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
