[POWERPC] Donate idle CPU cycles on dedicated partitions

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 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
have the 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.

Also rename the VPA's cpuctls_task_attrs field to a more accurate name.

Signed-off-by: Jake Moilanen <moilanen@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 470db6efaeb6..de6c2efd0479 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -399,6 +399,7 @@ static void pseries_dedicated_idle_sleep(void)
          * 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(void)
 
 out:
         HMT_medium();
+        get_lppaca()->donate_dedicated_cpu = 0;
         get_lppaca()->idle = 0;
 }