diff mbox

[16/19] powerpc: create giveup_all()

Message ID 1446079451-8774-17-git-send-email-anton@samba.org (mailing list archive)
State Accepted
Headers show

Commit Message

Anton Blanchard Oct. 29, 2015, 12:44 a.m. UTC 
Create a single function that gives everything up (FP, VMX, VSX, SPE).
Doing this all at once means we only do one MSR write.

A context switch microbenchmark using yield():

http://ozlabs.org/~anton/junkcode/context_switch2.c

./context_switch2 --test=yield --fp --altivec --vector 0 0

shows an improvement of 3% on POWER8.

Signed-off-by: Anton Blanchard <anton@samba.org>
---
 arch/powerpc/include/asm/switch_to.h |  1 +
 arch/powerpc/kernel/process.c        | 75 ++++++++++++++++++++++++++++--------
 arch/powerpc/kvm/book3s_pr.c         | 17 +-------
 3 files changed, 63 insertions(+), 30 deletions(-)

Comments

Michael Ellerman Dec. 2, 2015, 8:24 a.m. UTC | #1 
On Thu, 2015-10-29 at 11:44 +1100, Anton Blanchard wrote:

> Create a single function that gives everything up (FP, VMX, VSX, SPE).
> Doing this all at once means we only do one MSR write.
> 
> A context switch microbenchmark using yield():
> 
> http://ozlabs.org/~anton/junkcode/context_switch2.c
> 
> ./context_switch2 --test=yield --fp --altivec --vector 0 0
> 
> shows an improvement of 3% on POWER8.
> 
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>  arch/powerpc/include/asm/switch_to.h |  1 +
>  arch/powerpc/kernel/process.c        | 75 ++++++++++++++++++++++++++++--------
>  arch/powerpc/kvm/book3s_pr.c         | 17 +-------

books3s_pr.c can be a module, so we need giveup_all() to be EXPORT_SYMBOL.

I'll fix it up on my end.

cheers
diff mbox

Patch

diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index 9414dcb..8f85678 100644
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -26,6 +26,7 @@  extern void __giveup_vsx(struct task_struct *);
 extern void giveup_vsx(struct task_struct *);
 extern void enable_kernel_spe(void);
 extern void load_up_spe(struct task_struct *);
+extern void giveup_all(struct task_struct *);
 extern void switch_booke_debug_regs(struct debug_reg *new_debug);
 
 #ifdef CONFIG_PPC_FPU
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 9f8444b..a1540ee 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -308,6 +308,64 @@  void flush_spe_to_thread(struct task_struct *tsk)
 }
 #endif /* CONFIG_SPE */
 
+static unsigned long msr_all_available;
+
+static int __init init_msr_all_available(void)
+{
+#ifdef CONFIG_PPC_FPU
+	msr_all_available |= MSR_FP;
+#endif
+#ifdef CONFIG_ALTIVEC
+	if (cpu_has_feature(CPU_FTR_ALTIVEC))
+		msr_all_available |= MSR_VEC;
+#endif
+#ifdef CONFIG_VSX
+	if (cpu_has_feature(CPU_FTR_VSX))
+		msr_all_available |= MSR_VSX;
+#endif
+#ifdef CONFIG_SPE
+	if (cpu_has_feature(CPU_FTR_SPE))
+		msr_all_available |= MSR_SPE;
+#endif
+
+	return 0;
+}
+early_initcall(init_msr_all_available);
+
+void giveup_all(struct task_struct *tsk)
+{
+	unsigned long usermsr;
+
+	if (!tsk->thread.regs)
+		return;
+
+	usermsr = tsk->thread.regs->msr;
+
+	if ((usermsr & msr_all_available) == 0)
+		return;
+
+	msr_check_and_set(msr_all_available);
+
+#ifdef CONFIG_PPC_FPU
+	if (usermsr & MSR_FP)
+		__giveup_fpu(tsk);
+#endif
+#ifdef CONFIG_ALTIVEC
+	if (usermsr & MSR_VEC)
+		__giveup_altivec(tsk);
+#endif
+#ifdef CONFIG_VSX
+	if (usermsr & MSR_VSX)
+		__giveup_vsx(tsk);
+#endif
+#ifdef CONFIG_SPE
+	if (usermsr & MSR_SPE)
+		__giveup_spe(tsk);
+#endif
+
+	msr_check_and_clear(msr_all_available);
+}
+
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 void do_send_trap(struct pt_regs *regs, unsigned long address,
 		  unsigned long error_code, int signal_code, int breakpt)
@@ -839,21 +897,8 @@  struct task_struct *__switch_to(struct task_struct *prev,
 
 	__switch_to_tm(prev);
 
-	if (prev->thread.regs && (prev->thread.regs->msr & MSR_FP))
-		giveup_fpu(prev);
-#ifdef CONFIG_ALTIVEC
-	if (prev->thread.regs && (prev->thread.regs->msr & MSR_VEC))
-		giveup_altivec(prev);
-#endif /* CONFIG_ALTIVEC */
-#ifdef CONFIG_VSX
-	if (prev->thread.regs && (prev->thread.regs->msr & MSR_VSX))
-		/* VMX and FPU registers are already save here */
-		__giveup_vsx(prev);
-#endif /* CONFIG_VSX */
-#ifdef CONFIG_SPE
-	if ((prev->thread.regs && (prev->thread.regs->msr & MSR_SPE)))
-		giveup_spe(prev);
-#endif /* CONFIG_SPE */
+	/* Save FPU, Altivec, VSX and SPE state */
+	giveup_all(prev);
 
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 	switch_booke_debug_regs(&new->thread.debug);
diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 49f5dad..a78e0e6 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -1490,21 +1490,8 @@  static int kvmppc_vcpu_run_pr(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 		goto out;
 	/* interrupts now hard-disabled */
 
-	/* Save FPU state in thread_struct */
-	if (current->thread.regs->msr & MSR_FP)
-		giveup_fpu(current);
-
-#ifdef CONFIG_ALTIVEC
-	/* Save Altivec state in thread_struct */
-	if (current->thread.regs->msr & MSR_VEC)
-		giveup_altivec(current);
-#endif
-
-#ifdef CONFIG_VSX
-	/* Save VSX state in thread_struct */
-	if (current->thread.regs->msr & MSR_VSX)
-		__giveup_vsx(current);
-#endif
+	/* Save FPU, Altivec and VSX state */
+	giveup_all(current);
 
 	/* Preload FPU if it's enabled */
 	if (kvmppc_get_msr(vcpu) & MSR_FP)