[src/trunk]: src/sys/arch/arm/arm32 Must ... micro ... optimize!

[thorpej <thorpej%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/da6a76c97468
branches:  trunk
changeset: 535387:da6a76c97468
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Sat Aug 17 01:08:21 2002 +0000

description:
Must ... micro ... optimize!

* Save an instruction in the transition from idle to have-process-to-
  switch-to, and eliminate two instructions that cause datadep-stalls
  on StrongARM And XScale (one in each idle block).
* Rearrange some other instructions to avoid datadep-stalls on StrongARM
  and XScale.
* Since cpu_do_powersave == 0 is by far the common case, avoid a
  pipeline flush by reordering the two idle blocks.

diffstat:

 sys/arch/arm/arm32/cpuswitch.S |  40 +++++++++++++++++++++++-----------------
 1 files changed, 23 insertions(+), 17 deletions(-)

diffs (97 lines):

diff -r 3df3a7333edb -r da6a76c97468 sys/arch/arm/arm32/cpuswitch.S
--- a/sys/arch/arm/arm32/cpuswitch.S    Sat Aug 17 01:02:38 2002 +0000
+++ b/sys/arch/arm/arm32/cpuswitch.S    Sat Aug 17 01:08:21 2002 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: cpuswitch.S,v 1.15 2002/08/16 15:25:54 thorpej Exp $   */
+/*     $NetBSD: cpuswitch.S,v 1.16 2002/08/17 01:08:21 thorpej Exp $   */
 
 /*
  * Copyright (c) 1994-1998 Mark Brinicombe.
@@ -233,42 +233,45 @@
 
 /*
  * Idle loop, exercised while waiting for a process to wake up.
+ *
+ * NOTE: When we jump back to .Lswitch_search, we must have a
+ * pointer to whichqs in r7, which is what it is when we arrive
+ * here.
  */
 /* LINTSTUB: Ignore */
 ASENTRY_NP(idle)
 #if defined(LOCKDEBUG)
        bl      _C_LABEL(sched_unlock_idle)
 #endif
+       ldr     r3, .Lcpu_do_powersave
+
        /* Enable interrupts */
        IRQenable
 
        /* If we don't want to sleep, use a simpler loop. */
-       ldr     r3, .Lcpu_do_powersave
-       ldr     r7, Lwhichqs                    /* r7 = &whichqs */
-       ldr     r3, [r3]
+       ldr     r3, [r3]                /* r3 = cpu_do_powersave */
        teq     r3, #0
-       beq     .Lidle_nosleep
+       bne     2f
 
-       /* Powersave idle. */
+       /* Non-powersave idle. */
+1:     /* should maybe do uvm pageidlezero stuff here */
+       ldr     r3, [r7]                /* r3 = whichqs */
+       teq     r3, #0x00000000
+       bne     .Lswitch_search
+       b       1b
+
+2:     /* Powersave idle. */
        ldr     r4, Lcpufuncs
-.Lidle_sleep:
-       ldr     r3, [r7]
+3:     ldr     r3, [r7]                /* r3 = whichqs */
        teq     r3, #0x00000000
        bne     .Lswitch_search
 
        /* if saving power, don't want to pageidlezero */
        mov     r0, #0
-       add     lr, pc, #.Lidle_sleep - . - 8
+       add     lr, pc, #3b - . - 8
        ldr     pc, [r4, #(CF_SLEEP)]
        /* loops back around */
 
-       /* Non-powersave idle. */
-.Lidle_nosleep:
-       /* should maybe do uvm pageidlezero stuff here */
-       ldr     r3, [r7]
-       teq     r3, #0x00000000
-       bne     .Lswitch_search
-       b       .Lidle_nosleep
 
 /*
  * Find a new process to run, save the current context and
@@ -326,7 +329,10 @@
 
        /* First phase : find a new process */
 
+       ldr     r7, Lwhichqs
+
        /* rem: r5 = old proc */
+       /* rem: r7 = &whichqs */
 
 .Lswitch_search:
        IRQdisable
@@ -335,7 +341,6 @@
 #endif
 
        /* Do we have any active queues  */
-       ldr     r7, Lwhichqs
        ldr     r3, [r7]
 
        /* If not we must idle until we do. */
@@ -695,6 +700,7 @@
        mov     r0, #0x00000000
        str     r0, [r1]
 
+       ldr     r7, Lwhichqs            /* r7 = &whichqs */
        mov     r5, #0x00000000         /* r5 = old proc = NULL */
        b       .Lswitch_search