[PATCH 2/2] Donate dedicated CPU cycles

[Jake Moilanen <moilanen@austin.ibm.com>]

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.

The reason why shared processors just aren't used is because dedicated
CPUs are guaranteed an actual processor, yet the system is still able to
increase the capacity of the shared CPU pool.

Signed-off-by: Jake Moilanen <moilanen@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()->donate_dedicated_cpu = 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()->donate_dedicated_cpu = 0;
 	get_lppaca()->idle = 0;
 }