* [PATCH] powerpc: Clear RI and EE at the same time in system call exit
@ 2012-05-29 11:20 Anton Blanchard
2012-05-29 18:07 ` Scott Wood
0 siblings, 1 reply; 3+ messages in thread
From: Anton Blanchard @ 2012-05-29 11:20 UTC (permalink / raw)
To: benh, paulus, michael; +Cc: linuxppc-dev
In system call exit we currently clear RI and EE separately. An
mtmsrd is a slow operation and we can save cycles by doing it all
in one go.
This does complicate things a bit - we have to be careful to restore
RI if we branch out before returning to userspace.
On a POWER7 with virtual cputime disabled this patch improves the
null system call by 7%.
Signed-off-by: Anton Blanchard <anton@samba.org>
---
Index: linux-build/arch/powerpc/kernel/entry_64.S
===================================================================
--- linux-build.orig/arch/powerpc/kernel/entry_64.S 2012-05-28 18:23:33.374451416 +1000
+++ linux-build/arch/powerpc/kernel/entry_64.S 2012-05-29 21:18:22.280934940 +1000
@@ -197,7 +197,16 @@ syscall_exit:
wrteei 0
#else
ld r10,PACAKMSR(r13)
- mtmsrd r10,1
+ /*
+ * For performance reasons we clear RI the same time that we
+ * clear EE. We only need to clear RI just before we restore r13
+ * below, but batching it with EE saves us one expensive mtmsrd call.
+ * We have to be careful to restore RI if we branch anywhere from
+ * here (eg syscall_exit_work).
+ */
+ li r9,MSR_RI
+ andc r11,r10,r9
+ mtmsrd r11,1
#endif /* CONFIG_PPC_BOOK3E */
ld r9,TI_FLAGS(r12)
@@ -214,17 +223,6 @@ BEGIN_FTR_SECTION
END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
andi. r6,r8,MSR_PR
ld r4,_LINK(r1)
- /*
- * Clear RI before restoring r13. If we are returning to
- * userspace and we take an exception after restoring r13,
- * we end up corrupting the userspace r13 value.
- */
-#ifdef CONFIG_PPC_BOOK3S
- /* No MSR:RI on BookE */
- li r12,MSR_RI
- andc r11,r10,r12
- mtmsrd r11,1 /* clear MSR.RI */
-#endif /* CONFIG_PPC_BOOK3S */
beq- 1f
ACCOUNT_CPU_USER_EXIT(r11, r12)
@@ -271,6 +269,7 @@ syscall_enosys:
b syscall_exit
syscall_exit_work:
+ mtmsrd r10,1 /* Restore RI */
/* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr.
If TIF_NOERROR is set, just save r3 as it is. */
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] powerpc: Clear RI and EE at the same time in system call exit
2012-05-29 11:20 [PATCH] powerpc: Clear RI and EE at the same time in system call exit Anton Blanchard
@ 2012-05-29 18:07 ` Scott Wood
2012-05-29 22:22 ` Anton Blanchard
0 siblings, 1 reply; 3+ messages in thread
From: Scott Wood @ 2012-05-29 18:07 UTC (permalink / raw)
To: Anton Blanchard; +Cc: michael, paulus, linuxppc-dev
On 05/29/2012 06:20 AM, Anton Blanchard wrote:
>
> In system call exit we currently clear RI and EE separately. An
> mtmsrd is a slow operation and we can save cycles by doing it all
> in one go.
>
> This does complicate things a bit - we have to be careful to restore
> RI if we branch out before returning to userspace.
>
> On a POWER7 with virtual cputime disabled this patch improves the
> null system call by 7%.
>
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>
> Index: linux-build/arch/powerpc/kernel/entry_64.S
> ===================================================================
> --- linux-build.orig/arch/powerpc/kernel/entry_64.S 2012-05-28 18:23:33.374451416 +1000
> +++ linux-build/arch/powerpc/kernel/entry_64.S 2012-05-29 21:18:22.280934940 +1000
> @@ -197,7 +197,16 @@ syscall_exit:
> wrteei 0
> #else
> ld r10,PACAKMSR(r13)
> - mtmsrd r10,1
> + /*
> + * For performance reasons we clear RI the same time that we
> + * clear EE. We only need to clear RI just before we restore r13
> + * below, but batching it with EE saves us one expensive mtmsrd call.
> + * We have to be careful to restore RI if we branch anywhere from
> + * here (eg syscall_exit_work).
> + */
> + li r9,MSR_RI
> + andc r11,r10,r9
> + mtmsrd r11,1
> #endif /* CONFIG_PPC_BOOK3E */
>
> ld r9,TI_FLAGS(r12)
> @@ -214,17 +223,6 @@ BEGIN_FTR_SECTION
> END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
> andi. r6,r8,MSR_PR
> ld r4,_LINK(r1)
> - /*
> - * Clear RI before restoring r13. If we are returning to
> - * userspace and we take an exception after restoring r13,
> - * we end up corrupting the userspace r13 value.
> - */
> -#ifdef CONFIG_PPC_BOOK3S
> - /* No MSR:RI on BookE */
> - li r12,MSR_RI
> - andc r11,r10,r12
> - mtmsrd r11,1 /* clear MSR.RI */
> -#endif /* CONFIG_PPC_BOOK3S */
>
> beq- 1f
> ACCOUNT_CPU_USER_EXIT(r11, r12)
> @@ -271,6 +269,7 @@ syscall_enosys:
> b syscall_exit
>
> syscall_exit_work:
> + mtmsrd r10,1 /* Restore RI */
That mtmsrd needs an #ifdef CONFIG_PPC_BOOK3S
-Scott
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH] powerpc: Clear RI and EE at the same time in system call exit
2012-05-29 18:07 ` Scott Wood
@ 2012-05-29 22:22 ` Anton Blanchard
0 siblings, 0 replies; 3+ messages in thread
From: Anton Blanchard @ 2012-05-29 22:22 UTC (permalink / raw)
To: benh, paulus, michael, scottwood; +Cc: linuxppc-dev
Hi Scott,
> > syscall_exit_work:
> > + mtmsrd r10,1 /* Restore RI */
>
> That mtmsrd needs an #ifdef CONFIG_PPC_BOOK3S
Thanks!
Anton
--
In system call exit we currently clear RI and EE separately. An
mtmsrd is a slow operation and we can save cycles by doing it all
in one go.
This does complicate things a bit - we have to be careful to restore
RI if we branch out before returning to userspace.
On a POWER7 with virtual cputime disabled this patch improves the
null system call by 7%.
Signed-off-by: Anton Blanchard <anton@samba.org>
---
Index: linux-build/arch/powerpc/kernel/entry_64.S
===================================================================
--- linux-build.orig/arch/powerpc/kernel/entry_64.S 2012-05-29 21:22:40.293549055 +1000
+++ linux-build/arch/powerpc/kernel/entry_64.S 2012-05-30 07:47:31.380737406 +1000
@@ -197,7 +197,16 @@ syscall_exit:
wrteei 0
#else
ld r10,PACAKMSR(r13)
- mtmsrd r10,1
+ /*
+ * For performance reasons we clear RI the same time that we
+ * clear EE. We only need to clear RI just before we restore r13
+ * below, but batching it with EE saves us one expensive mtmsrd call.
+ * We have to be careful to restore RI if we branch anywhere from
+ * here (eg syscall_exit_work).
+ */
+ li r9,MSR_RI
+ andc r11,r10,r9
+ mtmsrd r11,1
#endif /* CONFIG_PPC_BOOK3E */
ld r9,TI_FLAGS(r12)
@@ -214,17 +223,6 @@ BEGIN_FTR_SECTION
END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
andi. r6,r8,MSR_PR
ld r4,_LINK(r1)
- /*
- * Clear RI before restoring r13. If we are returning to
- * userspace and we take an exception after restoring r13,
- * we end up corrupting the userspace r13 value.
- */
-#ifdef CONFIG_PPC_BOOK3S
- /* No MSR:RI on BookE */
- li r12,MSR_RI
- andc r11,r10,r12
- mtmsrd r11,1 /* clear MSR.RI */
-#endif /* CONFIG_PPC_BOOK3S */
beq- 1f
ACCOUNT_CPU_USER_EXIT(r11, r12)
@@ -271,6 +269,9 @@ syscall_enosys:
b syscall_exit
syscall_exit_work:
+#ifdef CONFIG_PPC_BOOK3S
+ mtmsrd r10,1 /* Restore RI */
+#endif
/* If TIF_RESTOREALL is set, don't scribble on either r3 or ccr.
If TIF_NOERROR is set, just save r3 as it is. */
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2012-05-29 22:22 UTC | newest]
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2012-05-29 18:07 ` Scott Wood
2012-05-29 22:22 ` Anton Blanchard
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