sh: Minor optimisations to FPU handling
A number of small optimisations to FPU handling, in particular:
- move the task USEDFPU flag from the thread_info flags field (which
is accessed asynchronously to the thread) to a new status field,
which is only accessed by the thread itself. This allows locking to
be removed in most cases, or can be reduced to a preempt_lock().
This mimics the i386 behaviour.
- move the modification of regs->sr and thread_info->status flags out
of save_fpu() to __unlazy_fpu(). This gives the compiler a better
chance to optimise things, as well as making save_fpu() symmetrical
with restore_fpu() and init_fpu().
- implement prepare_to_copy(), so that when creating a thread, we can
unlazy the FPU prior to copying the thread data structures.
Also make sure that the FPU is disabled while in the kernel, in
particular while booting, and for newly created kernel threads,
In a very artificial benchmark, the execution time for 2500000
context switches was reduced from 50 to 45 seconds.
Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
diff --git a/arch/sh/include/asm/processor_32.h b/arch/sh/include/asm/processor_32.h
index 9a87149..1f3d6fa 100644
--- a/arch/sh/include/asm/processor_32.h
+++ b/arch/sh/include/asm/processor_32.h
@@ -56,6 +56,7 @@
#define SR_DSP 0x00001000
#define SR_IMASK 0x000000f0
#define SR_FD 0x00008000
+#define SR_MD 0x40000000
/*
* DSP structure and data
@@ -136,7 +137,7 @@
extern void release_thread(struct task_struct *);
/* Prepare to copy thread state - unlazy all lazy status */
-#define prepare_to_copy(tsk) do { } while (0)
+void prepare_to_copy(struct task_struct *tsk);
/*
* create a kernel thread without removing it from tasklists