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 <an...@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. */
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