Module Name: src
Committed By: riastradh
Date: Wed Mar 1 08:18:13 UTC 2023
Modified Files:
src/sys/arch/powerpc/powerpc: locore_subr.S
Log Message:
powerpc: Optimization: Omit needless membar when triggering softint.
When we are triggering a softint, it can't already hold any mutexes.
So any path to mutex_exit(mtx) must go via mutex_enter(mtx), which is
always done with atomic r/m/w, and we need not issue any explicit
barrier between ci->ci_curlwp = softlwp and a potential load of
mtx->mtx_owner in mutex_exit.
PR kern/57240
XXX pullup-8
XXX pullup-9
XXX pullup-10
To generate a diff of this commit:
cvs rdiff -u -r1.67 -r1.68 src/sys/arch/powerpc/powerpc/locore_subr.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/powerpc/powerpc/locore_subr.S
diff -u src/sys/arch/powerpc/powerpc/locore_subr.S:1.67 src/sys/arch/powerpc/powerpc/locore_subr.S:1.68
--- src/sys/arch/powerpc/powerpc/locore_subr.S:1.67 Thu Feb 23 14:56:11 2023
+++ src/sys/arch/powerpc/powerpc/locore_subr.S Wed Mar 1 08:18:13 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: locore_subr.S,v 1.67 2023/02/23 14:56:11 riastradh Exp $ */
+/* $NetBSD: locore_subr.S,v 1.68 2023/03/01 08:18:13 riastradh Exp $ */
/*
* Copyright (c) 2001 Wasabi Systems, Inc.
@@ -418,9 +418,13 @@ _ENTRY(softint_fast_dispatch)
sync /* XXX eieio */ /* for mutex_enter; see cpu_switchto */
#endif
stptr %r3, CI_CURLWP(%r7)
-#ifdef MULTIPROCESSOR
- sync /* for mutex_enter; see cpu_switchto */
-#endif
+ /*
+ * No need for barrier after ci->ci_curlwp = softlwp -- when we
+ * enter a softint lwp, it can't be holding any mutexes, so it
+ * can't release any until after it has acquired them, so we
+ * need not participate in the protocol with mutex_vector_enter
+ * barriers here.
+ */
mr %r13, %r3
#ifdef PPC_BOOKE
mtsprg2 %r3
