| wdenk | b02744a | 2003-04-05 00:53:31 +0000 | [diff] [blame] | 1 | Notes on the scheduler in sched.c: |
| 2 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 3 | |
| 4 | 'sched.c' provides an very simplistic multi-threading scheduler. |
| 5 | See the example, function 'sched(...)', in the same file for its |
| 6 | API usage. |
| 7 | |
| 8 | Until an exhaustive testing can be done, the implementation cannot |
| 9 | qualify as that of production quality. It works with the example |
| 10 | in 'sched.c', it may or may not work in other cases. |
| 11 | |
| 12 | |
| 13 | Limitations: |
| 14 | ~~~~~~~~~~~~ |
| 15 | |
| 16 | - There are NO primitives for thread synchronization (locking, |
| 17 | notify etc). |
| 18 | |
| 19 | - Only the GPRs and FPRs context is saved during a thread context |
| 20 | switch. Other registers on the PowerPC processor (60x, 7xx, 7xxx |
| 21 | etc) are NOT saved. |
| 22 | |
| 23 | - The scheduler is NOT transparent to the user. The user |
| 24 | applications must invoke thread_yield() to allow other threads to |
| 25 | scheduler. |
| 26 | |
| 27 | - There are NO priorities, and the scheduling policy is round-robin |
| 28 | based. |
| 29 | |
| 30 | - There are NO capabilities to collect thread CPU usage, scheduler |
| 31 | stats, thread status etc. |
| 32 | |
| 33 | - The semantics are somewhat based on those of pthreads, but NOT |
| 34 | the same. |
| 35 | |
| 36 | - Only seven threads are allowed. These can be easily increased by |
| 37 | changing "#define MAX_THREADS" depending on the available memory. |
| 38 | |
| 39 | - The stack size of each thread is 8KBytes. This can be easily |
| 40 | increased depending on the requirement and the available memory, |
| 41 | by increasing "#define STK_SIZE". |
| 42 | |
| 43 | - Only one master/parent thread is allowed, and it cannot be |
| 44 | stopped or deleted. Any given thread is NOT allowed to stop or |
| 45 | delete itself. |
| 46 | |
| 47 | - There NOT enough safety checks as are probably in the other |
| 48 | threads implementations. |
| 49 | |
| 50 | - There is no parent-child relationship between threads. Only one |
| 51 | thread may thread_join, preferably the master/parent thread. |
| 52 | |
| 53 | (C) 2003 Arun Dharankar <ADharankar@ATTBI.Com> |