Module: xenomai-gch
Branch: for-forge
Commit: dec18d7dfa7981ff7c2d7414ea30db968a86136c
URL:
http://git.xenomai.org/?p=xenomai-gch.git;a=commit;h=dec18d7dfa7981ff7c2d7414ea30db968a86136c
Author: Gilles Chanteperdrix <gilles.chanteperd...@xenomai.org>
Date: Fri Oct 25 21:53:56 2013 +0200
cobalt/x86: lazy FPU switching
Only enable XNFPU on first FPU use.
Skip context restore with fxsr when context allows it.
---
kernel/cobalt/arch/x86/thread.c | 33 +++++++++++++++++++++++++--------
1 file changed, 25 insertions(+), 8 deletions(-)
diff --git a/kernel/cobalt/arch/x86/thread.c b/kernel/cobalt/arch/x86/thread.c
index 1bbac8a..d181d60 100644
--- a/kernel/cobalt/arch/x86/thread.c
+++ b/kernel/cobalt/arch/x86/thread.c
@@ -225,7 +225,7 @@ int xnarch_handle_fpu_fault(struct xnthread *from,
struct xnarchtcb *tcb = xnthread_archtcb(to);
struct task_struct *p = tcb->core.host_task;
- if (tsk_used_math(p))
+ if (wrap_test_fpu_used(p))
return 0;
/*
@@ -243,6 +243,7 @@ int xnarch_handle_fpu_fault(struct xnthread *from,
set_stopped_child_used_math(p);
wrap_set_fpu_used(p);
+ xnthread_set_state(to, XNFPU);
return 1;
}
@@ -273,10 +274,9 @@ void xnarch_save_fpu(struct xnthread *thread)
struct task_struct *p = tcb->core.host_task;
if (wrap_test_fpu_used(p) == 0)
- /* Common case: already saved by __switch_to */
+ /* Saved by last __switch_to */
return;
- /* Exceptional case: a migrating thread */
clts();
__do_save_i387(x86_fpustate_ptr(&p->thread));
@@ -287,11 +287,24 @@ void xnarch_switch_fpu(struct xnthread *from, struct
xnthread *thread)
{
struct xnarchtcb *tcb = xnthread_archtcb(thread);
struct task_struct *p = tcb->core.host_task;
+ const unsigned root_kfpu = tcb->root_kfpu;
+ unsigned do_restore;
- if (tcb->root_kfpu == 0 &&
- (tsk_used_math(p) == 0 || xnthread_test_state(thread, XNROOT)))
+ if (root_kfpu == 0) {
/* Restore lazy mode */
- return;
+ if (xnthread_test_state(thread, XNROOT))
+ return;
+
+ /*
+ * If we never switched fpu, and the cpu has fxsr, the
+ * last context switch saved fpu but did not
+ * reinitialize it, so we can simply reenable fpu
+ */
+ do_restore = (from != thread &&
+ (!from || from->tcb.fpup != thread->tcb.fpup)) ||
+ cpu_has_fxsr == 0;
+ } else
+ do_restore = 1;
/*
* Restore the FPU hardware with valid fp registers from a
@@ -299,8 +312,9 @@ void xnarch_switch_fpu(struct xnthread *from, struct
xnthread *thread)
*/
clts();
- __do_restore_i387(x86_fpustate_ptr(&p->thread));
- if (tcb->root_kfpu) {
+ if (do_restore)
+ __do_restore_i387(x86_fpustate_ptr(&p->thread));
+ if (root_kfpu) {
x86_fpustate_ptr(&p->thread) = tcb->fpup;
wrap_clear_fpu_used(p);
if (tcb->root_used_math == 0)
@@ -335,6 +349,9 @@ void xnarch_init_shadow_tcb(struct xnthread *thread)
#endif
tcb->fpup = x86_fpustate_ptr(&p->thread);
tcb->root_kfpu = 0;
+
+ /* XNFPU is set upon first FPU fault */
+ xnthread_clear_state(thread, XNFPU);
}
int xnarch_escalate(void)
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