Module Name: src
Committed By: thorpej
Date: Thu Jul 22 15:48:40 UTC 2021
Modified Files:
src/sys/arch/alpha/alpha: locore.s
Log Message:
It's unlikely that a process will be using restartable atomic sequences
on Alpha, and furthermore it's unlikely that any given context switch
will be returning to one even if the process has them. So, re-arrange
the RAS processing in cpu_switchto() so that the most likely code paths
are predicted by the branch predictor. On an EV4-class processor, this
will save ~4-6 cycles on just about every context switch.
To generate a diff of this commit:
cvs rdiff -u -r1.140 -r1.141 src/sys/arch/alpha/alpha/locore.s
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/alpha/alpha/locore.s
diff -u src/sys/arch/alpha/alpha/locore.s:1.140 src/sys/arch/alpha/alpha/locore.s:1.141
--- src/sys/arch/alpha/alpha/locore.s:1.140 Sun Jul 11 01:55:51 2021
+++ src/sys/arch/alpha/alpha/locore.s Thu Jul 22 15:48:40 2021
@@ -1,4 +1,4 @@
-/* $NetBSD: locore.s,v 1.140 2021/07/11 01:55:51 thorpej Exp $ */
+/* $NetBSD: locore.s,v 1.141 2021/07/22 15:48:40 thorpej Exp $ */
/*-
* Copyright (c) 1999, 2000, 2019 The NetBSD Foundation, Inc.
@@ -67,7 +67,7 @@
#include <machine/asm.h>
-__KERNEL_RCSID(0, "$NetBSD: locore.s,v 1.140 2021/07/11 01:55:51 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: locore.s,v 1.141 2021/07/22 15:48:40 thorpej Exp $");
#include "assym.h"
@@ -844,14 +844,7 @@ LEAF(cpu_switchto, 0)
*/
ldq a0, L_PROC(s2) /* first ras_lookup() arg */
ldq t0, P_RASLIST(a0) /* any RAS entries? */
- beq t0, 2f /* no, skip */
- ldq s1, L_MD_TF(s2) /* s1 = l->l_md.md_tf */
- ldq a1, (FRAME_PC*8)(s1) /* second ras_lookup() arg */
- CALL(ras_lookup) /* ras_lookup(p, PC) */
- addq v0, 1, t0 /* -1 means "not in ras" */
- beq t0, 2f
- stq v0, (FRAME_PC*8)(s1)
-
+ bne t0, 4f /* yes, go deal with it */
2:
mov s4, v0 /* return the old lwp */
/*
@@ -883,6 +876,16 @@ LEAF(cpu_switchto, 0)
stq sp, PCB_HWPCB_KSP(a3) /* save old SP */
ldq sp, PCB_HWPCB_KSP(a2) /* restore new SP */
br 1b /* finish up */
+
+4:
+ ldq s1, L_MD_TF(s2) /* s1 = l->l_md.md_tf */
+ ldq a1, (FRAME_PC*8)(s1) /* second ras_lookup() arg */
+ CALL(ras_lookup) /* ras_lookup(p, PC) */
+ addq v0, 1, t0 /* -1 means "not in ras" */
+ beq t0, 2b /* not in ras? return */
+ stq v0, (FRAME_PC*8)(s1) /* in ras? fix up PC */
+ br 2b /* finish up */
+
END(cpu_switchto)
/*
