Re: Inter Module communication

[Jon Masters <jonmasters@xxxxxxxxx>]

On Fri, 1 Oct 2004 00:07:24 +0530, Dhiman, Gaurav <gaurav.dhiman@xxxxxx> wrote:

> If anybody else knows some other synchronizing mechanism in kernel, then
> please do mail about that.

There are reader-writer versions of the locking primitives that you
describe below. Linux 2.6 also introduces two new locking types:

    *). Completion variables - tasks often use this to sync up their actions.
    *). Seq locks - simple retry locks (but as rml points out, they do
favour writers).

> Semaphore: This is a heavy synchronizing mechanism and should be used if
> our critical section is big enough ......

There's a fundamental distinction between semaphores and spinlocks you
need to note - semaphores only work in a process context as they may
sleep. With the preempt stuff on in the kernel we have to worry about
more than just SMP systems, but spinlocks will still disable
pre-emption if necessary by changing preempt_count for us.

Jon.

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