Author: mjg
Date: Wed Aug 28 19:40:57 2019
New Revision: 351577
URL: https://svnweb.freebsd.org/changeset/base/351577
Log:
amd64: clean up cpu_switch.S
- LK macro (conditional on SMP for the lock prefix) is unused
- SETLK unnecessarily performs xchg. obtained value is never used and the
implicit lock prefix adds avoidable cost. Barrier provided by it does
not appear to be of any use.
- the lock waited for is almost never blocked, yet the loop starts with
a pause. Move it out of the common case.
Reviewed by: kib
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D19563
Modified:
head/sys/amd64/amd64/cpu_switch.S
Modified: head/sys/amd64/amd64/cpu_switch.S
==============================================================================
--- head/sys/amd64/amd64/cpu_switch.S Wed Aug 28 19:28:27 2019
(r351576)
+++ head/sys/amd64/amd64/cpu_switch.S Wed Aug 28 19:40:57 2019
(r351577)
@@ -45,18 +45,6 @@
.text
-#ifdef SMP
-#define LK lock ;
-#else
-#define LK
-#endif
-
-#if defined(SCHED_ULE) && defined(SMP)
-#define SETLK xchgq
-#else
-#define SETLK movq
-#endif
-
/*
* cpu_throw()
*
@@ -150,17 +138,15 @@ ctx_switch_xsave:
movq %rdx,%r15
movq %rsi,%rdi
callq pmap_activate_sw
- SETLK %r15,TD_LOCK(%r13) /* Release the old thread */
+ movq %r15,TD_LOCK(%r13) /* Release the old thread */
sw1:
movq TD_PCB(%r12),%r8
#if defined(SCHED_ULE) && defined(SMP)
- /* Wait for the new thread to become unblocked */
movq $blocked_lock, %rdx
-1:
movq TD_LOCK(%r12),%rcx
cmpq %rcx, %rdx
- pause
- je 1b
+ je sw1wait
+sw1cont:
#endif
/*
* At this point, we've switched address spaces and are ready
@@ -496,3 +482,14 @@ ENTRY(resumectx)
xorl %eax,%eax
ret
END(resumectx)
+
+/* Wait for the new thread to become unblocked */
+#if defined(SCHED_ULE) && defined(SMP)
+sw1wait:
+1:
+ pause
+ movq TD_LOCK(%r12),%rcx
+ cmpq %rcx, %rdx
+ je 1b
+ jmp sw1cont
+#endif
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