powerpc: Per process DSCR + some fixes (try#4)

The DSCR (aka Data Stream Control Register) is supported on some
server PowerPC chips and allow some control over the prefetch
of data streams.

This patch allows the value to be specified per thread by emulating
the corresponding mfspr and mtspr instructions. Children of such
threads inherit the value. Other threads use a default value that
can be specified in sysfs - /sys/devices/system/cpu/dscr_default.

If a thread starts with non default value in the sysfs entry,
all children threads inherit this non default value even if
the sysfs value is changed later.

Signed-off-by: Alexey Kardashevskiy <aik@au1.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/emulated_ops.h b/arch/powerpc/include/asm/emulated_ops.h
index f0fb4fc1f6e6..45921672b97a 100644
--- a/arch/powerpc/include/asm/emulated_ops.h
+++ b/arch/powerpc/include/asm/emulated_ops.h
@@ -52,6 +52,10 @@ extern struct ppc_emulated {
 #ifdef CONFIG_VSX
         struct ppc_emulated_entry vsx;
 #endif
+#ifdef CONFIG_PPC64
+        struct ppc_emulated_entry mfdscr;
+        struct ppc_emulated_entry mtdscr;
+#endif
 } ppc_emulated;
 
 extern u32 ppc_warn_emulated;