From d04075478d378d9e15f3e1abfd14b0bd124077d4 Mon Sep 17 00:00:00 2001 From: Kevin Date: Sat, 15 Nov 2014 11:48:36 +0800 Subject: init commit via android 4.4 uboot --- doc/README.sched | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100755 doc/README.sched (limited to 'doc/README.sched') diff --git a/doc/README.sched b/doc/README.sched new file mode 100755 index 0000000..3aa89e6 --- /dev/null +++ b/doc/README.sched @@ -0,0 +1,53 @@ +Notes on the scheduler in sched.c: +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + + 'sched.c' provides an very simplistic multi-threading scheduler. + See the example, function 'sched(...)', in the same file for its + API usage. + + Until an exhaustive testing can be done, the implementation cannot + qualify as that of production quality. It works with the example + in 'sched.c', it may or may not work in other cases. + + +Limitations: +~~~~~~~~~~~~ + + - There are NO primitives for thread synchronization (locking, + notify etc). + + - Only the GPRs and FPRs context is saved during a thread context + switch. Other registers on the PowerPC processor (60x, 7xx, 7xxx + etc) are NOT saved. + + - The scheduler is NOT transparent to the user. The user + applications must invoke thread_yield() to allow other threads to + scheduler. + + - There are NO priorities, and the scheduling policy is round-robin + based. + + - There are NO capabilities to collect thread CPU usage, scheduler + stats, thread status etc. + + - The semantics are somewhat based on those of pthreads, but NOT + the same. + + - Only seven threads are allowed. These can be easily increased by + changing "#define MAX_THREADS" depending on the available memory. + + - The stack size of each thread is 8KBytes. This can be easily + increased depending on the requirement and the available memory, + by increasing "#define STK_SIZE". + + - Only one master/parent thread is allowed, and it cannot be + stopped or deleted. Any given thread is NOT allowed to stop or + delete itself. + + - There NOT enough safety checks as are probably in the other + threads implementations. + + - There is no parent-child relationship between threads. Only one + thread may thread_join, preferably the master/parent thread. + +(C) 2003 Arun Dharankar -- cgit