From: David van Moolenbroek <david@minix3.org>
Date: Sat, 3 Mar 2012 19:33:02 +0000 (+0100)
Subject: Kernel: only reset/reload FPU state when necessary
X-Git-Url: http://zhaoyanbai.com/repos/%22http:/www.isc.org/icons/zlib_tech.html?a=commitdiff_plain;h=784af1207446cb107229858b2ecd7d5ef2488d9a;p=minix.git

Kernel: only reset/reload FPU state when necessary
---

diff --git a/kernel/arch/i386/arch_system.c b/kernel/arch/i386/arch_system.c
index be8503a57..455490273 100644
--- a/kernel/arch/i386/arch_system.c
+++ b/kernel/arch/i386/arch_system.c
@@ -274,24 +274,27 @@ PUBLIC void fpu_init(void)
         }
 }
 
-PUBLIC void save_local_fpu(struct proc *pr)
+PUBLIC void save_local_fpu(struct proc *pr, int retain)
 {
+	/* Save process FPU context. If the 'retain' flag is set, keep the FPU
+	 * state as is. If the flag is not set, the state is undefined upon
+	 * return, and the caller is responsible for reloading a proper state.
+	 */
+
 	if(!is_fpu())
 		return;
 
-	/* Save changed FPU context. */
 	if(osfxsr_feature) {
 		fxsave(pr->p_fpu_state.fpu_save_area_p);
-		fninit();
 	} else {
 		fnsave(pr->p_fpu_state.fpu_save_area_p);
+		if (retain)
+			(void) frstor(pr->p_fpu_state.fpu_save_area_p);
 	}
 }
 
 PUBLIC void save_fpu(struct proc *pr)
 {
-	int r;
-
 #ifdef CONFIG_SMP
 	if (cpuid != pr->p_cpu) {
 		int stopped;
@@ -316,13 +319,7 @@ PUBLIC void save_fpu(struct proc *pr)
 
 	if (get_cpulocal_var(fpu_owner) == pr) {
 		disable_fpu_exception();
-		save_local_fpu(pr);
-
-		/* The state may now be reset, and the caller does not expect
-		 * this. Immediately restore the saved state.
-		 */
-		r = restore_fpu(pr);
-		assert(r == OK);
+		save_local_fpu(pr, TRUE /*retain*/);
 	}
 }
 
diff --git a/kernel/proc.c b/kernel/proc.c
index d385e4349..4595f08c2 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -1878,7 +1878,7 @@ PUBLIC void copr_not_available_handler(void)
 	local_fpu_owner = get_cpulocal_var_ptr(fpu_owner);
 	if (*local_fpu_owner != NULL) {
 		assert(*local_fpu_owner != p);
-		save_local_fpu(*local_fpu_owner);
+		save_local_fpu(*local_fpu_owner, FALSE /*retain*/);
 	}
 
 	/*
@@ -1889,7 +1889,7 @@ PUBLIC void copr_not_available_handler(void)
 		/* Restoring FPU state failed. This is always the process's own
 		 * fault. Send a signal, and schedule another process instead.
 		 */
-		*local_fpu_owner = NULL;
+		*local_fpu_owner = NULL;		/* release FPU */
 		cause_sig(proc_nr(p), SIGFPE);
 		return;
 	}
diff --git a/kernel/proto.h b/kernel/proto.h
index e3f3a9f09..a8288063f 100644
--- a/kernel/proto.h
+++ b/kernel/proto.h
@@ -34,7 +34,7 @@ _PROTOTYPE( void context_stop, (struct proc * p)			);
 _PROTOTYPE( void context_stop_idle, (void)				);
 _PROTOTYPE( int restore_fpu, (struct proc *)				);
 _PROTOTYPE( void save_fpu, (struct proc *)				);
-_PROTOTYPE( void save_local_fpu, (struct proc *)			);
+_PROTOTYPE( void save_local_fpu, (struct proc *, int retain)		);
 _PROTOTYPE( void fpu_sigcontext, (struct proc *, struct sigframe *fr, struct sigcontext *sc)	);
 
 /* main.c */
diff --git a/kernel/smp.c b/kernel/smp.c
index 8a521f474..8e2d097e5 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -168,12 +168,12 @@ PUBLIC void smp_sched_handler(void)
 			RTS_SET(p, RTS_PROC_STOP);
 		}
 		if (flgs & SCHED_IPI_SAVE_CTX) {
-			/* all context have been save already,  FPU remains */
+			/* all context has been saved already, FPU remains */
 			if (proc_used_fpu(p) &&
 					get_cpulocal_var(fpu_owner) == p) {
 				disable_fpu_exception();
-				save_local_fpu(p);
-				/* we re preparing to migrate somewhere else */
+				save_local_fpu(p, FALSE /*retain*/);
+				/* we're preparing to migrate somewhere else */
 				release_fpu(p);
 			}
 		}