linux-kernel - [PATCH 5/8] x86,fpu: introduce task_disable_lazy_fpu

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Date:	Fri,  6 Feb 2015 15:02:02 -0500
From:	riel@...hat.com
To:	oleg@...hat.com
Cc:	dave.hansen@...ux.intel.com, sbsiddha@...il.com,
	luto@...capital.net, tglx@...utronix.de, mingo@...nel.org,
	hpa@...or.com, fenghua.yu@...el.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 5/8] x86,fpu: introduce task_disable_lazy_fpu_restore helper

From: Rik van Riel <riel@...hat.com>

Currently there are a few magic assignments sprinkled through the
code that disable lazy FPU state restoring, some more effective than
others, and all equally mystifying.

It would be easier to have a helper to explicitly disable lazy
FPU state restoring for a task.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 arch/x86/include/asm/fpu-internal.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index 439ac3921a1e..c1f66261ad12 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -79,6 +79,16 @@ static inline void __cpu_disable_lazy_restore(unsigned int cpu)
 	per_cpu(fpu_owner_task, cpu) = NULL;
 }
 
+/*
+ * Used to indicate that the FPU state in memory is newer than the FPU
+ * state in registers, and the FPU state should be reloaded next time the
+ * task is run. Only safe on the current task, or non-running tasks.
+ */
+static inline void task_disable_lazy_fpu_restore(struct task_struct *tsk)
+{
+	tsk->thread.fpu.last_cpu = ~0;
+}
+
 static inline int fpu_lazy_restore(struct task_struct *new, unsigned int cpu)
 {
 	return new == this_cpu_read_stable(fpu_owner_task) &&
-- 
1.9.3

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