b09bcf6779
In this second phase, scheduling is moved from PM to its own scheduler (see r6557 for phase one). In the next phase we hope to a) include useful information in the "out of quantum" message and b) create some simple scheduling policy that makes use of that information. When the system starts up, PM will iterate over its process table and ask SCHED to take over scheduling unprivileged processes. This is done by sending a SCHEDULING_START message to SCHED. This message includes the processes endpoint, the parent's endpoint and its nice level. The scheduler adds this process to its schedproc table, issues a schedctl, and returns its own endpoint to PM - as the endpoint of the effective scheduler. When a process terminates, a SCHEDULING_STOP message is sent to the scheduler. The reason for this effective endpoint is for future compatibility. Some day, we may have a scheduler that, instead of scheduling the process itself, forwards the SCHEDULING_START message on to another scheduler. PM has information on who schedules whom. As such, scheduling messages from user-land are sent through PM. An example is when processes change their priority, using nice(). In that case, a getsetpriority message is sent to PM, which then sends a SCHEDULING_SET_NICE to the process's effective scheduler. When a process is forked through PM, it inherits its parent's scheduler, but is spawned with an empty quantum. As before, a request to fork a process flows through VM before returning to PM, which then wakes up the child process. This flow has been modified slightly so that PM notifies the scheduler of the new process, before waking up the child process. If the scheduler fails to take over scheduling, the child process is torn down and the fork fails with an erroneous value. Process priority is entirely decided upon using nice levels. PM stores a copy of each process's nice level and when a child is forked, its parent's nice level is sent in the SCHEDULING_START message. How this level is mapped to a priority queue is up to the scheduler. It should be noted that the nice level is used to determine the max_priority and the parent could have been in a lower priority when it was spawned. To prevent a CPU intensive process from hawking the CPU by continuously forking children that get scheduled in the max_priority, the scheduler should determine in which queue the parent is currently scheduled, and schedule the child in that same queue. Other fixes: The USER_Q in kernel/proc.h was incorrectly defined as NR_SCHED_QUEUES/2. That results in a "off by one" error when converting priority->nice->priority for nice=0. This also had the side effect that if someone were to set the MAX_USER_Q to something else than 0, then USER_Q would be off.
120 lines
3.3 KiB
C
120 lines
3.3 KiB
C
/* This file contains the main program of the SCHED scheduler. It will sit idle
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* until asked, by PM, to take over scheduling a particular process.
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*/
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/* The _MAIN def indicates that we want the schedproc structs to be created
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* here. Used from within schedproc.h */
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#define _MAIN
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#include "sched.h"
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#include "schedproc.h"
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/* Declare some local functions. */
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FORWARD _PROTOTYPE( void reply, (endpoint_t whom, message *m_ptr) );
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FORWARD _PROTOTYPE( void sef_local_startup, (void) );
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/*===========================================================================*
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* main *
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*===========================================================================*/
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PUBLIC int main(void)
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{
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/* Main routine of the scheduler. */
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message m_in; /* the incoming message itself is kept here. */
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int call_nr; /* system call number */
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int who_e; /* caller's endpoint */
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int result; /* result to system call */
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int rv;
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/* SEF local startup. */
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sef_local_startup();
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/* Initialize scheduling timers, used for running balance_queues */
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init_scheduling();
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/* This is SCHED's main loop - get work and do it, forever and forever. */
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while (TRUE) {
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int ipc_status;
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/* Wait for the next message and extract useful information from it. */
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if (sef_receive_status(ANY, &m_in, &ipc_status) != OK)
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panic("SCHED sef_receive error");
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who_e = m_in.m_source; /* who sent the message */
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call_nr = m_in.m_type; /* system call number */
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/* Check for system notifications first. Special cases. */
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if (is_ipc_notify(ipc_status)) {
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switch(who_e) {
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case CLOCK:
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sched_expire_timers(m_in.NOTIFY_TIMESTAMP);
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continue; /* don't reply */
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default :
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result = ENOSYS;
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}
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goto sendreply;
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}
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switch(call_nr) {
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case SCHEDULING_START:
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result = do_start_scheduling(&m_in);
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break;
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case SCHEDULING_STOP:
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result = do_stop_scheduling(&m_in);
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break;
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case SCHEDULING_SET_NICE:
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result = do_nice(&m_in);
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break;
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case SCHEDULING_NO_QUANTUM:
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/* This message was sent from the kernel, don't reply */
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if (IPC_STATUS_FLAGS_TEST(ipc_status,
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IPC_FLG_MSG_FROM_KERNEL)) {
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if ((rv = do_noquantum(&m_in)) != (OK)) {
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printf("SCHED: Warning, do_noquantum "
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"failed with %d\n", rv);
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}
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continue; /* Don't reply */
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}
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else {
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printf("SCHED: process %d faked "
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"SCHEDULING_NO_QUANTUM message!\n",
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who_e);
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result = EPERM;
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}
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break;
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default:
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result = no_sys(who_e, call_nr);
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}
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sendreply:
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/* Send reply. */
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if (result != SUSPEND) {
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m_in.m_type = result; /* build reply message */
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reply(who_e, &m_in); /* send it away */
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}
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}
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return(OK);
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}
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/*===========================================================================*
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* reply *
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*===========================================================================*/
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PRIVATE void reply(endpoint_t who_e, message *m_ptr)
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{
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int s = send(who_e, m_ptr); /* send the message */
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if (OK != s)
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printf("SCHED: unable to send reply to %d: %d\n", who_e, s);
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}
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/*===========================================================================*
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* sef_local_startup *
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*===========================================================================*/
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PRIVATE void sef_local_startup(void)
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{
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/* No init callbacks for now. */
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/* No live update support for now. */
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/* No signal callbacks for now. */
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/* Let SEF perform startup. */
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sef_startup();
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}
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