Hi, On Tue, Mar 29 2011, NamJae Jeon wrote: > Dear. Chris, Ben. > > Thanks for your reply. > > As you know, booting time is important factor in embededd device. > > If rootdelay is set to 5, kernel will be waiting for 5 sec. root_wait > is also looping per 100ms. No. It will wait for *up to* five seconds, but it will actually continue as soon as the device has enumerated. Same with rootwait, of course. MMC is by no means the only subsystem that behaves this way. If you were using a USB or SATA/AHCI device, amongst many others, you would have exactly the same problem. You can see http://lwn.net/Articles/330378/ for some background reading. > I have a question. Why is mmc using delayed workqueue ? So that device enumeration can happen in the background, without delaying the kernel boot while we wait for the controller to get all the way to creating partitions. If we didn't use a workqueue and you were working on an embedded project that had an MMC slot that it *didn't* boot from, you'd be yelling at us for instead wasting time holding up your non-mmc boot by not letting userspace get going until we list MMC partitions. We can't win. :-) In any case, I suspect that your system actually does boot faster than it would if we didn't use a workqueue -- this way the delays in waiting for the controller to come up are parallelized with other boot code. That's good, right? - Chris. -- Chris Ball <cjb@xxxxxxxxxx> <http://printf.net/> One Laptop Per Child -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
