Re: [PATCH] scheduler patch, faster still

Rik van Riel (H.H.vanRiel@phys.uu.nl)
Sun, 27 Sep 1998 19:22:36 +0200 (CEST)

On Sun, 27 Sep 1998, Michael L. Galbraith wrote:
> On Sun, 27 Sep 1998, Rik van Riel wrote:
>
> > Here is a second version of my scheduler patch. It
> > should improve RT latency a little bit and remove
> > overhead with programs waiting very shortly on things
> > like IPC or buffer cache locks...
>
> <g> how about a patch for sendmail so that if it sees [PATCH] in a
> subject line, it refuses to send unless you did include the patch.

Seems like a good idea :)

Anyway, here it is.

(there shouldn't be much difference anyway, except for lower
overhead and faster RT response)

Rik.
+-------------------------------------------------------------------+
| Linux memory management tour guide. H.H.vanRiel@phys.uu.nl |
| Scouting Vries cubscout leader. http://www.phys.uu.nl/~riel/ |
+-------------------------------------------------------------------+

--- linux-2.1.122/include/linux/sched.h Fri Sep 25 16:44:06 1998
+++ linux-local/include/linux/sched.h Sun Sep 27 15:17:49 1998
@@ -259,6 +259,7 @@

struct wait_queue *wait_chldexit; /* for wait4() */
unsigned long timeout, policy, rt_priority;
+ unsigned long sleep_time; /* when did we go to sleep? */
unsigned long it_real_value, it_prof_value, it_virt_value;
unsigned long it_real_incr, it_prof_incr, it_virt_incr;
struct timer_list real_timer;
@@ -270,7 +271,6 @@
int swappable:1;
unsigned long swap_address;
unsigned long old_maj_flt; /* old value of maj_flt */
- unsigned long dec_flt; /* page fault count of the last time */
unsigned long swap_cnt; /* number of pages to swap on next pass */
/* process credentials */
uid_t uid,euid,suid,fsuid;
@@ -348,12 +348,12 @@
/* pidhash */ NULL, NULL, \
/* tarray */ &task[0], \
/* chld wait */ NULL, \
-/* timeout */ 0,SCHED_OTHER,0,0,0,0,0,0,0, \
+/* timeout */ 0,SCHED_OTHER,0,0,0,0,0,0,0,0, \
/* timer */ { NULL, NULL, 0, 0, it_real_fn }, \
/* utime */ {0,0,0,0},0, \
/* per CPU times */ {0, }, {0, }, \
/* flt */ 0,0,0,0,0,0, \
-/* swp */ 0,0,0,0,0, \
+/* swp */ 0,0,0,0, \
/* process credentials */ \
/* uid etc */ 0,0,0,0,0,0,0,0, \
/* suppl grps*/ 0, {0,}, \
--- linux-2.1.122/kernel/sched.c Fri Sep 25 16:43:12 1998
+++ linux-local/kernel/sched.c Sun Sep 27 17:13:35 1998
@@ -157,6 +157,14 @@
{
struct task_struct *next = init_task.next_run;

+ if (p->policy != SCHED_OTHER || p->sleep_time == jiffies)
+ goto fastpath;
+ p->counter += ((jiffies - p->sleep_time) * p->priority) / DEF_PRIORITY;
+ /* if we sleep 'too long' or if jiffies overflows, the value
+ will be normalized here (p->counter is signed) */
+ if (p->counter > 2 * p->priority || p->counter < 0)
+ p->counter = 2 * p->priority;
+fastpath:
p->prev_run = &init_task;
init_task.next_run = p;
p->next_run = next;
@@ -173,6 +181,7 @@
prev->next_run = next;
p->next_run = NULL;
p->prev_run = NULL;
+ p->sleep_time = jiffies;
}

static inline void move_last_runqueue(struct task_struct * p)
@@ -537,8 +546,12 @@
if (!c) {
struct task_struct *p;
read_lock(&tasklist_lock);
- for_each_task(p)
+ p = init_task.next_run;
+ while (p != &init_task) {
+ /* maybe someone added a task, keep the p->counter */
p->counter = (p->counter >> 1) + p->priority;
+ p = p->next_run;
+ }
read_unlock(&tasklist_lock);
}
}

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