From: Ingo Molnar <mingo@kernel.org>
Date: Mon, 27 Apr 2015 07:45:12 +0000 (+0200)
Subject: x86/fpu: Optimize fpu__save()
X-Git-Tag: omap-for-v4.3/legacy-v2-signed~203^2~106
X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=48c4717f30cc1f83d02f045c3b47a2885863bff2;p=pandora-kernel.git

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>
---

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