Hi,
This diff makes sure that a proc and its per-CPU structure which tracks when to
schedule another proc in round-robin are in sync. No observable change in time
spent compiling the bsd.mp kernel.
This diff in addition with another which replaces schedclock() with equivalent
code, shaves approx 5 secs in real time from a bsd.mp kernel build.
Thanks
Index: kern/sched_bsd.c
===================================================================
RCS file: /cvs/src/sys/kern/sched_bsd.c,v
retrieving revision 1.62
diff -u -p -u -p -r1.62 sched_bsd.c
--- kern/sched_bsd.c 30 Jan 2020 08:51:27 -0000 1.62
+++ kern/sched_bsd.c 11 Feb 2020 14:00:17 -0000
@@ -90,21 +90,13 @@ roundrobin(struct cpu_info *ci)
{
struct schedstate_percpu *spc = &ci->ci_schedstate;
- spc->spc_rrticks = rrticks_init;
-
if (ci->ci_curproc != NULL) {
- if (spc->spc_schedflags & SPCF_SEENRR) {
- /*
- * The process has already been through a roundrobin
- * without switching and may be hogging the CPU.
- * Indicate that the process should yield.
- */
- atomic_setbits_int(&spc->spc_schedflags,
- SPCF_SHOULDYIELD);
- } else {
- atomic_setbits_int(&spc->spc_schedflags,
- SPCF_SEENRR);
- }
+ /*
+ * The process is now completing a roundrobin
+ * without switching off the CPU and may be hogging the CPU.
+ * Indicate that the process should yield.
+ */
+ atomic_setbits_int(&spc->spc_schedflags, SPCF_SHOULDYIELD);
}
if (spc->spc_nrun)
@@ -384,6 +376,16 @@ mi_switch(void)
* scheduling flags.
*/
atomic_clearbits_int(&spc->spc_schedflags, SPCF_SWITCHCLEAR);
+
+ /*
+ * We start afresh here, sync the proc and the per-cpu state
+ * to match exactly on how much time to allow the proc to run.
+ * This gives a chance to a proc to get its full quantum, and
+ * not worry if there is a chance to have it taken off the CPU
+ * at way less than its alloted quantum or have another proc
+ * take way more than its alloted quantum.
+ */
+ spc->spc_rrticks = rrticks_init;
nextproc = sched_chooseproc();
Index: sys/sched.h
===================================================================
RCS file: /cvs/src/sys/sys/sched.h,v
retrieving revision 1.56
diff -u -p -u -p -r1.56 sched.h
--- sys/sched.h 21 Oct 2019 10:24:01 -0000 1.56
+++ sys/sched.h 11 Feb 2020 14:00:17 -0000
@@ -131,9 +131,8 @@ struct cpustats {
#ifdef _KERNEL
/* spc_flags */
-#define SPCF_SEENRR 0x0001 /* process has seen roundrobin() */
#define SPCF_SHOULDYIELD 0x0002 /* process should yield the CPU */
-#define SPCF_SWITCHCLEAR (SPCF_SEENRR|SPCF_SHOULDYIELD)
+#define SPCF_SWITCHCLEAR (SPCF_SHOULDYIELD)
#define SPCF_SHOULDHALT 0x0004 /* CPU should be vacated */
#define SPCF_HALTED 0x0008 /* CPU has been halted */
