[PATCH] Donate dedicated CPU cycles

[Jake Moilanen]

A Power6 can give up CPU cycles on a dedicated CPU (as opposed to a
shared CPU) to other shared processors if the administrator asks for it
(via the HMC).

This patch enables that to work properly on P6.

This just involves setting a bit in the CAS structure as well as the
VPA.  To donate cycles, a CPU has to have all SMT threads idle and w/
donate bit set in the VPA.  Then call H_CEDE.

Signed-off-by: Jake Moilanen <moilanen at austin.ibm.com>

--
 arch/powerpc/kernel/prom_init.c        |    4 +++-
 arch/powerpc/platforms/pseries/setup.c |    2 ++
 2 files changed, 5 insertions(+), 1 deletion(-)

Index: powerpc/arch/powerpc/kernel/prom_init.c
===================================================================
--- powerpc.orig/arch/powerpc/kernel/prom_init.c
+++ powerpc/arch/powerpc/kernel/prom_init.c
@@ -635,6 +635,7 @@ static void __init early_cmdline_parse(v
 /* ibm,dynamic-reconfiguration-memory property supported */
 #define OV5_DRCONF_MEMORY	0x20
 #define OV5_LARGE_PAGES		0x10	/* large pages supported */
+#define OV5_DONATE_DEDICATE_CPU 0x02	/* donate dedicated CPU support */
 /* PCIe/MSI support.  Without MSI full PCIe is not supported */
 #ifdef CONFIG_PCI_MSI
 #define OV5_MSI			0x01	/* PCIe/MSI support */
@@ -685,7 +686,8 @@ static unsigned char ibm_architecture_ve
 	/* option vector 5: PAPR/OF options */
 	3 - 2,				/* length */
 	0,				/* don't ignore, don't halt */
-	OV5_LPAR | OV5_SPLPAR | OV5_LARGE_PAGES | OV5_DRCONF_MEMORY | OV5_MSI,
+	OV5_LPAR | OV5_SPLPAR | OV5_LARGE_PAGES | OV5_DRCONF_MEMORY |
+	OV5_DONATE_DEDICATE_CPU | OV5_MSI,
 };
 
 /* Old method - ELF header with PT_NOTE sections */
Index: powerpc/arch/powerpc/platforms/pseries/setup.c
===================================================================
--- powerpc.orig/arch/powerpc/platforms/pseries/setup.c
+++ powerpc/arch/powerpc/platforms/pseries/setup.c
@@ -399,6 +399,7 @@ static void pseries_dedicated_idle_sleep
 	 * a good time to find other work to dispatch.
 	 */
 	get_lppaca()->idle = 1;
+	get_lppaca()->cpuctls_task_attrs = 1;
 
 	/*
 	 * We come in with interrupts disabled, and need_resched()
@@ -431,6 +432,7 @@ static void pseries_dedicated_idle_sleep
 
 out:
 	HMT_medium();
+	get_lppaca()->cpuctls_task_attrs = 0;
 	get_lppaca()->idle = 0;
 }