On Wed, 8 Oct 2003, Emmanuel ALLAUD wrote:
> Juliusz Chroboczek wrote:
>
> >>>I'd like to suggest that you implement device-specific code as a kernel
> >>>module.
> >>>
> >>>
> >
> >Well, that won't happen; we already have working portable driver code
> >in userspace, and there's no chance we'll port that to the Linux kernel.
> >
> >On the other hand, I do think that we'll end up using more kernel-side
> >functionality than we currently do; perhaps someday we'll have enough
> >of that to be able to run non-root servers, at least on hardware that
> >does memory-mapped I/O (the iopl system call is for root only).
> >
> >TR> The key problem with this is that kernel modules are Linux-specific, and
> >TR> further often need to be kernel-version specific. XFree86 runs quite well
> >TR> in many non-Linux environments today.
> >
> >But that doesn't prevent it from using features specific to Linux when
> >needed. Notice for example the use of the vm86old syscall in the
> >Linux/i386 version of the int10 module, or the (optional) use of fbdev
> >in quite a few drivers, or the future use of the /dev/input/event
> >devices (hint, hint). Let alone the DRI.
> >
> >
> >
> >>>Implementing a kernel module might give access to more resources, like
> >>>tighter console control, asynchronous accelerations,
> >>>
> >>>
> >
> >TR> No, I don't think any of that is true.
> >
> >DMA? Smarter polling of FIFO status? Retrace interrupt?
> >
> >
> For this specific problem : I talked with M. Vojkovich about the
> yielding problem in that case, then we brought this to linux kernel guys
> (R. Russel and R. Love), both agreed to say that using sched_yield()
> will be really incorrect in 2.6, certainly to too much latency. They
> also both agreed to say that the solution is to use futex to sync the
> user space driver with the help of a kernel side which would poll the
> FIFO status (or whatever other conditions we want to wait for). They
> seemed to be interested in supporting that, so perhaps a joint effort
> could be successful on both sides so kernel can provide new services the
> X server could use.
> Bye
> Manu
This is more of a hack than a solution. I still see little utility
in a kernel module.
Mark.
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