From 48c4717f30cc1f83d02f045c3b47a2885863bff2 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@kernel.org>
Date: Mon, 27 Apr 2015 09:45:12 +0200
Subject: [PATCH] x86/fpu: Optimize fpu__save()
So fpu__save() does this currently:
copy_fpregs_to_fpstate(fpu);
if (!use_eager_fpu())
fpregs_deactivate(fpu);
... which deactivates the FPU on lazy switching systems unconditionally.
Both usecases of fpu__save() use this function to save the
FPU state into a fpstate: fork()/clone() and math error signal handling.
The unconditional disabling of FPU registers in the lazy switching
case is probably a mistaken conversion of old FNSAVE code (that had
to disable FPU registers).
So speed up this code by only disabling FPU registers when absolutely
necessary: when indicated by the copy_fpregs_to_fpstate() return
code:
if (!copy_fpregs_to_fpstate(fpu))
fpregs_deactivate(fpu);
Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/fpu/core.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index a0b2221b686d2..b1fbbb8eb934c 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -170,7 +170,7 @@ void irq_ts_restore(int TS_state)
EXPORT_SYMBOL_GPL(irq_ts_restore);
/*
- * Save the FPU state (initialize it if necessary):
+ * Save the FPU state (mark it for reload if necessary):
*
* This only ever gets called for the current task.
*/
@@ -180,8 +180,7 @@ void fpu__save(struct fpu *fpu)
preempt_disable();
if (fpu->fpregs_active) {
- copy_fpregs_to_fpstate(fpu);
- if (!use_eager_fpu())
+ if (!copy_fpregs_to_fpstate(fpu))
fpregs_deactivate(fpu);
}
preempt_enable();
--
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