---

yaml
---
r: 158715
b: refs/heads/master
c: 17950c5
h: refs/heads/master
i:
  158713: 4f0364b
  158711: 5b204d5
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 16d9dbf0c2bd167fdd942b83592d59696c7b73bd
+refs/heads/master: 17950c5b243f99cbabef173415ee988c52104d7e

trunk/arch/x86/kernel/process_64.c

@@ -386,9 +386,17 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	int cpu = smp_processor_id();
 	struct tss_struct *tss = &per_cpu(init_tss, cpu);
 	unsigned fsindex, gsindex;
+	bool preload_fpu;
+
+	/*
+	 * If the task has used fpu the last 5 timeslices, just do a full
+	 * restore of the math state immediately to avoid the trap; the
+	 * chances of needing FPU soon are obviously high now
+	 */
+	preload_fpu = tsk_used_math(next_p) && next_p->fpu_counter > 5;
 
 	/* we're going to use this soon, after a few expensive things */
-	if (next_p->fpu_counter > 5)
+	if (preload_fpu)
 		prefetch(next->xstate);
 
 	/*
@@ -422,6 +430,10 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	/* Must be after DS reload */
 	unlazy_fpu(prev_p);
 
+	/* Make sure cpu is ready for new context */
+	if (preload_fpu)
+		clts();
+
 	/*
 	 * Leave lazy mode, flushing any hypercalls made here.
 	 * This must be done before restoring TLS segments so
@@ -480,15 +492,12 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 		     task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
 		__switch_to_xtra(prev_p, next_p, tss);
 
-	/* If the task has used fpu the last 5 timeslices, just do a full
-	 * restore of the math state immediately to avoid the trap; the
-	 * chances of needing FPU soon are obviously high now
-	 *
-	 * tsk_used_math() checks prevent calling math_state_restore(),
-	 * which can sleep in the case of !tsk_used_math()
+	/*
+	 * Preload the FPU context, now that we've determined that the
+	 * task is likely to be using it. 
 	 */
-	if (tsk_used_math(next_p) && next_p->fpu_counter > 5)
-		math_state_restore();
+	if (preload_fpu)
+		__math_state_restore();
 	return prev_p;
 }