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x86/fpu: Optimize fpu__save()

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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>
This commit is contained in:
Ingo Molnar 2015-04-27 09:45:12 +02:00
parent fea435a202
commit 48c4717f30
1 changed files with 2 additions and 3 deletions
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5
arch/x86/kernel/fpu/core.c
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@ -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();