schedcpu, uvm_meter(9): make uvm_meter() an independent timeout

uvm_meter(9) should not base its periodic uvm_loadav() call on the UTC
clock.  It also no longer needs to periodically wake up proc0 because
proc0 doesn't do any work.  schedcpu() itself may change or go away,
but as kettenis@ notes we probably can't completely remove the concept
of a "load average" from OpenBSD, given its long Unix heritage.

So, (1) remove the uvm_meter() call from schedcpu(), (2) make
uvm_meter() an independent timeout started alongside schedcpu() during
scheduler_start(), and (3) delete the vestigial periodic proc0 wakeup.

With input from deraadt@, kettenis@, and claudio@.  deraadt@ cautions
that this change may confuse administrators who hold the load average
in high regard.

Thread: https://marc.info/?l=openbsd-tech&m=168710929409153&w=2

general agreement with this direction from kettenis@
ok claudio@

diff --git a/share/man/man9/uvm_init.9 b/share/man/man9/uvm_init.9
index 2ef1769..636a16a 100644 (file)
--- a/share/man/man9/uvm_init.9
+++ b/share/man/man9/uvm_init.9
@@ -1,4 +1,4 @@
-.\"    $OpenBSD: uvm_init.9,v 1.5 2023/05/21 05:11:38 jmc Exp $
+.\"    $OpenBSD: uvm_init.9,v 1.6 2023/06/20 16:30:30 cheloha Exp $
 .\"    $NetBSD: uvm.9,v 1.14 2000/06/29 06:08:44 mrg Exp $
 .\"
 .\" Copyright (c) 1998 Matthew R. Green
@@ -28,7 +28,7 @@
 .\" XXX this manual sets nS to 1 or 0 in the description, to obtain
 .\" synopsis-like function prototypes.  any better way?
 .\"
-.Dd $Mdocdate: May 21 2023 $
+.Dd $Mdocdate: June 20 2023 $
 .Dt UVM_INIT 9
 .Os
 .Sh NAME
@@ -168,7 +168,7 @@ argument is ignored.
 .Ft void
 .Fn uvm_kernacc "caddr_t addr" "size_t len" "int rw"
 .Ft void
-.Fn uvm_meter
+.Fn uvm_meter "void *"
 .Ft int
 .Fn uvm_sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp " "size_t newlen" "struct proc *p"
 .Ft int
@@ -212,7 +212,7 @@ access, in the kernel address space.
 .Pp
 The
 .Fn uvm_meter
-function calculates the load average and wakes up the swapper if necessary.
+function periodically recomputes the load average.
 .Pp
 The
 .Fn uvm_sysctl

diff --git a/sys/kern/sched_bsd.c b/sys/kern/sched_bsd.c
index 94d0950..3a82cca 100644 (file)
--- a/sys/kern/sched_bsd.c
+++ b/sys/kern/sched_bsd.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: sched_bsd.c,v 1.74 2023/02/04 19:33:03 cheloha Exp $  */
+/*     $OpenBSD: sched_bsd.c,v 1.75 2023/06/20 16:30:30 cheloha Exp $  */
 /*     $NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $ */
 
 /*-
@@ -234,7 +234,6 @@ schedcpu(void *arg)
                }
                SCHED_UNLOCK(s);
        }
-       uvm_meter();
        wakeup(&lbolt);
        timeout_add_sec(to, 1);
 }
@@ -669,6 +668,7 @@ scheduler_start(void)
 
        rrticks_init = hz / 10;
        schedcpu(&schedcpu_to);
+       uvm_meter(NULL);
 
 #ifndef SMALL_KERNEL
        if (perfpolicy == PERFPOL_AUTO)

diff --git a/sys/uvm/uvm_extern.h b/sys/uvm/uvm_extern.h
index 702d9b9..85124bd 100644 (file)
--- a/sys/uvm/uvm_extern.h
+++ b/sys/uvm/uvm_extern.h
@@ -1,4 +1,4 @@
-/*     $OpenBSD: uvm_extern.h,v 1.168 2023/05/30 08:30:01 jsg Exp $    */
+/*     $OpenBSD: uvm_extern.h,v 1.169 2023/06/20 16:30:30 cheloha Exp $        */
 /*     $NetBSD: uvm_extern.h,v 1.57 2001/03/09 01:02:12 chs Exp $      */
 
 /*
@@ -414,7 +414,7 @@ void                        uvmspace_free(struct vmspace *);
 struct vmspace         *uvmspace_share(struct process *);
 int                    uvm_share(vm_map_t, vaddr_t, vm_prot_t,
                            vm_map_t, vaddr_t, vsize_t);
-void                   uvm_meter(void);
+void                   uvm_meter(void *);
 int                    uvm_sysctl(int *, u_int, void *, size_t *, 
                            void *, size_t, struct proc *);
 struct vm_page         *uvm_pagealloc(struct uvm_object *,

diff --git a/sys/uvm/uvm_meter.c b/sys/uvm/uvm_meter.c
index f86fb03..8fc7c10 100644 (file)
--- a/sys/uvm/uvm_meter.c
+++ b/sys/uvm/uvm_meter.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: uvm_meter.c,v 1.42 2020/12/28 14:01:23 mpi Exp $      */
+/*     $OpenBSD: uvm_meter.c,v 1.43 2023/06/20 16:30:30 cheloha Exp $  */
 /*     $NetBSD: uvm_meter.c,v 1.21 2001/07/14 06:36:03 matt Exp $      */
 
 /*
@@ -65,6 +65,9 @@
 int maxslp = MAXSLP;   /* patchable ... */
 struct loadavg averunnable;
 
+#define UVM_METER_INTVL        5
+struct timeout uvm_meter_to = TIMEOUT_INITIALIZER(uvm_meter, NULL);
+
 /*
  * constants for averages over 1, 5, and 15 minutes when sampling at
  * 5 second intervals.
@@ -82,15 +85,13 @@ void uvm_total(struct vmtotal *);
 void uvmexp_read(struct uvmexp *);
 
 /*
- * uvm_meter: calculate load average and wake up the swapper (if needed)
+ * uvm_meter: recompute load averages
  */
 void
-uvm_meter(void)
+uvm_meter(void *unused)
 {
-       if ((gettime() % 5) == 0)
-               uvm_loadav(&averunnable);
-       if (proc0.p_slptime > (maxslp / 2))
-               wakeup(&proc0);
+       timeout_add_sec(&uvm_meter_to, UVM_METER_INTVL);
+       uvm_loadav(&averunnable);
 }
 
 /*