Messages in this thread | | | Date | Fri, 21 Mar 2003 17:38:00 -0800 | From | Greg KH <> | Subject | Re: [PATCH] alternative dev patch |
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On Fri, Mar 21, 2003 at 10:08:43AM +0100, Roman Zippel wrote: > Hi, > > On Thu, 20 Mar 2003, Greg KH wrote: > > > On Fri, Mar 21, 2003 at 12:03:57AM +0100, Roman Zippel wrote: > > > I'm unsure how your code will scale. It depends on how that code will be > > > used. If drivers register a lot of devices, your lookup function has to > > > scan a possibly very long list of minor devices and that function is > > > difficult to optimize. > > > > And then we grab the BKL :( > > This is currently required for either implementation and needs to be moved > to the driver.
Heh, that is definiatly a 2.7 thing, too many drivers rely on this functionality :(
> > Hint, optimizing the open() path for char devices is not anything we > > will probably be doing in 2.6, due to the BKL usage there. It's also > > not anything anyone has seen on any known benchmarks as a point of > > contention, so I would not really worry about this for now. > > The BKL also shouldn't be a reason to make it unnecessary expensive? I > don't understand your argument.
I was trying to point out that pre-mature optimiziation of this code should not be done before we get rid of the most expensive portion, the bkl. That's all.
> > > char devices don't have partitions, so you hardly need regions. The > > > problem with the tty layer is that the console and the serial devices > > > should have different majors. > > > > There are a number of char drivers that have "regions". The tty layer > > support them, and the usb core supports them as two examples. I'm sure > > there are others. Personally, I like the symmetry with the block device > > function the way Andries did it. > > Every single call to usb_register_dev in 2.5.65 uses exactly 1 minor > number. Block device drivers need regions because they have partitions > and we need to find out which device a partition belongs to. Where have > character devices such requirements?
Oh yeah, I forgot I had cleaned up that api to not reserve minors in chunks, sorry. It used to do that :)
So only tty drivers currently do this. But that might just be because it's pretty hard to get a range of minors right now, as the api hasn't been present. Once we expand the range, I bet it will get quite common (most character drivers only want from 1-16 minors normally.)
> > > only needed to generate /proc/misc. As soon as character devices are > > > better integrated into the driver model, even this list is not needed > > > anymore. This means for simple character devices, we can easily add a > > > alloc_chardev/add_chardev interface similiar to block devices. > > > > No, I don't see /proc/misc going away due to the driver model, I imagine > > there are too many users of it to disappear. Also, the driver model > > doesn't care a thing about major/minor numbers so I don't understand how > > you think it can help in this situation. > > I didn't mean that /proc/misc goes away, I meant the misc_list in misc.c. > They could be other ways to generate /proc/misc. > /proc/devices, /proc/misc, /proc/tty/drivers, ... is currently mostly > needed to generate device nodes for dynamic device numbers. This badly > needs a more generic mechanism.
I agree. But again, 2.7. Remember our feature freeze?
thanks,
greg k-h - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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