[linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

[Timothy Miller]

Lee Revell wrote:

> There are still a few areas that need work, ioctl gives me problems, but
> the latest 2.6 kernels are quite good.  If you look at the 'clean'
> version of the voluntary kernel preemption patch it is pretty small.  My
> understanding is that the kernel is already preemptible anytime that a
> spin lock (including the BKL) is not held, and that the voluntary kernel
> preemption patch adds some scheduling points in places where it is safe
> to sleep, but preemption is disabled because we are holding the BKL, and
> that the number of these should approach zero as the kernel is improved
> anyway.


That's confusing to me.  It was my understanding that the BKL is used to 
completely lock down the kernel so that no other CPU can have a process 
get into the kernel... something like how SMP was done under 2.0.

So, if you sleep during a BKL, wouldn't that imply that nothing else 
would be allowed to enter the kernel until after the kernel thread that 
took the lock wakes up and releases the lock?