Messages in this thread | | | Date | Tue, 25 Jul 2006 14:27:10 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [RFC PATCH] Multi-threaded device probing |
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Greg KH wrote: > During the kernel summit, I was reminded by the wish by some people to > do device probing in parallel, so I created the following patch. It > offers up the ability for the driver core to create a new thread for > every driver<->device probe call. To enable this, the driver needs to > have the multithread_probe flag set to 1, otherwise the "traditional" > sequencial probe happens. > > Note that this patch does not actually enable the threaded probe for any > busses, as that's very dangerous at this point in time, without the > different bus authors trying it out and verifying that it does work > properly. > > I did enable this for both USB and PCI and shaved .4 seconds off of the > boot time of my tiny little single processor laptop. The savings of my > 4-way workstation is much greater, but things start to happen so fast we > miss the root disk, as init starts before the disks are finished being > initialized. I have some hacks to work around this right now, but I'll > hold off on posting them before I make sure they work properly (breaking > booting of people's machines isn't the best way to get them to accept > new features...) > > Anyway, have fun playing around with this if you want, I'll be adding > this to the next -mm, but you will have to enable the bit on your own if > you want to see any speedups. >
This is very interesting in the context of a few discussions I had at OLS about klibc; there are people who would like initramfs to be accessible *before* device probing is done, so that drivers can access firmware and possible hotplug from the initramfs during the driver initialization. We could even invoke (k)init at this point; this would require a) having a system call or device that would allow kinit to block until device probing was complete, and b) a way to handle /dev/console -- there are several different ways to deal with it; it's mostly a matter of picking a good one.
Note that we don't need device drivers for userspace -- we only need VM, VFS and scheduler initialization.
Multithreaded device initialization is a great idea, especially since many devices require delays during initialization, sometimes on the order of seconds.
-hpa
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