Documentation: create new scheduler/ subdirectory

The top-level Documentation/ directory is unmanageably large, so we
should take any obvious opportunities to move stuff into subdirectories.
These sched-*.txt files seem an obvious easy case.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 89 deletions

diff --git a/Documentation/sched-arch.txt b/Documentation/sched-arch.txt
deleted file mode 100644
index 941615a..0000000
--- a/Documentation/sched-arch.txt
+++ /dev/null
@@ -1,89 +0,0 @@
-	CPU Scheduler implementation hints for architecture specific code
-
-	Nick Piggin, 2005
-
-Context switch
-==============
-1. Runqueue locking
-By default, the switch_to arch function is called with the runqueue
-locked. This is usually not a problem unless switch_to may need to
-take the runqueue lock. This is usually due to a wake up operation in
-the context switch. See include/asm-ia64/system.h for an example.
-
-To request the scheduler call switch_to with the runqueue unlocked,
-you must `#define __ARCH_WANT_UNLOCKED_CTXSW` in a header file
-(typically the one where switch_to is defined).
-
-Unlocked context switches introduce only a very minor performance
-penalty to the core scheduler implementation in the CONFIG_SMP case.
-
-2. Interrupt status
-By default, the switch_to arch function is called with interrupts
-disabled. Interrupts may be enabled over the call if it is likely to
-introduce a significant interrupt latency by adding the line
-`#define __ARCH_WANT_INTERRUPTS_ON_CTXSW` in the same place as for
-unlocked context switches. This define also implies
-`__ARCH_WANT_UNLOCKED_CTXSW`. See include/asm-arm/system.h for an
-example.
-
-
-CPU idle
-========
-Your cpu_idle routines need to obey the following rules:
-
-1. Preempt should now disabled over idle routines. Should only
-   be enabled to call schedule() then disabled again.
-
-2. need_resched/TIF_NEED_RESCHED is only ever set, and will never
-   be cleared until the running task has called schedule(). Idle
-   threads need only ever query need_resched, and may never set or
-   clear it.
-
-3. When cpu_idle finds (need_resched() == 'true'), it should call
-   schedule(). It should not call schedule() otherwise.
-
-4. The only time interrupts need to be disabled when checking
-   need_resched is if we are about to sleep the processor until
-   the next interrupt (this doesn't provide any protection of
-   need_resched, it prevents losing an interrupt).
-
-	4a. Common problem with this type of sleep appears to be:
-	        local_irq_disable();
-	        if (!need_resched()) {
-	                local_irq_enable();
-	                *** resched interrupt arrives here ***
-	                __asm__("sleep until next interrupt");
-	        }
-
-5. TIF_POLLING_NRFLAG can be set by idle routines that do not
-   need an interrupt to wake them up when need_resched goes high.
-   In other words, they must be periodically polling need_resched,
-   although it may be reasonable to do some background work or enter
-   a low CPU priority.
-
-   	5a. If TIF_POLLING_NRFLAG is set, and we do decide to enter
-	    an interrupt sleep, it needs to be cleared then a memory
-	    barrier issued (followed by a test of need_resched with
-	    interrupts disabled, as explained in 3).
-
-arch/i386/kernel/process.c has examples of both polling and
-sleeping idle functions.
-
-
-Possible arch/ problems
-=======================
-
-Possible arch problems I found (and either tried to fix or didn't):
-
-h8300 - Is such sleeping racy vs interrupts? (See #4a).
-        The H8/300 manual I found indicates yes, however disabling IRQs
-        over the sleep mean only NMIs can wake it up, so can't fix easily
-        without doing spin waiting.
-
-ia64 - is safe_halt call racy vs interrupts? (does it sleep?) (See #4a)
-
-sh64 - Is sleeping racy vs interrupts? (See #4a)
-
-sparc - IRQs on at this point(?), change local_irq_save to _disable.
-      - TODO: needs secondary CPUs to disable preempt (See #1)
-