Commit-ID: 48c4717f30cc1f83d02f045c3b47a2885863bff2
Gitweb: http://git.kernel.org/tip/48c4717f30cc1f83d02f045c3b47a2885863bff2
Author: Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate: Mon, 27 Apr 2015 09:45:12 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 19 May 2015 15:47:53 +0200
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@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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 a0b2221..b1fbbb8 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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