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SubjectRe: Schedule idle

On Tue, 10 Nov 1998, Gordon P. Oliver wrote:

> _please_ We can do better than this. Only semaphores (not spinlocks) need
> to have the priority inheritance. [...]

nope there are _not_ only semaphores, but many other types of locks.

> [...] This can be done with lists off the
> semaphore and tasks... [...]

it's _not_ easy to extend Linux semaphores to handle priority inheritance.
currently semaphore operations can be done via hw-atomic test-and-set
instructions. If we do anything more complex, we cannot use simple
instructions anymore. Linux semaphores are 2 instructions for an up() and
2 for a down(), and thats one of our crown jewels :)

the whole point is not quite valid, RT and filesystem IO doesnt mix well
anyway ... the solution: use system calls that are guaranteed to not
block, either by design, or by system policy (ie. separate filesystem on a
RAMDISK) ... or use a device that doesnt introduce large latencies.
(RAMdisk or solid state disk)

-- mingo


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