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Subject[PATCH 86/93] powerpc: Default arch idle could cede processor on pseries
Date
3.8.13.10 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>

commit 363edbe2614aa90df706c0f19ccfa2a6c06af0be upstream.

When adding cpuidle support to pSeries, we introduced two
regressions:

- The new cpuidle backend driver only works under hypervisors
supporting the "SLPLAR" option, which isn't the case of the
old POWER4 hypervisor and the HV "light" used on js2x blades

- The cpuidle driver registers fairly late, meaning that for
a significant portion of the boot process, we end up having
all threads spinning. This slows down the boot process and
increases the overall resource usage if the hypervisor has
shared processors.

This fixes both by implementing a "default" idle that will cede
to the hypervisor when possible, in a very simple way without
all the bells and whisles of cpuidle.

Reported-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Acked-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
arch/powerpc/platforms/pseries/setup.c | 31 +++++++++++++++++++++----------
1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index ca55882..28f6ccd 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -353,7 +353,7 @@ static int alloc_dispatch_log_kmem_cache(void)
}
early_initcall(alloc_dispatch_log_kmem_cache);

-static void pSeries_idle(void)
+static void pseries_lpar_idle(void)
{
/* This would call on the cpuidle framework, and the back-end pseries
* driver to go to idle states
@@ -361,10 +361,22 @@ static void pSeries_idle(void)
if (cpuidle_idle_call()) {
/* On error, execute default handler
* to go into low thread priority and possibly
- * low power mode.
+ * low power mode by cedeing processor to hypervisor
*/
- HMT_low();
- HMT_very_low();
+
+ /* Indicate to hypervisor that we are idle. */
+ get_lppaca()->idle = 1;
+
+ /*
+ * Yield the processor to the hypervisor. We return if
+ * an external interrupt occurs (which are driven prior
+ * to returning here) or if a prod occurs from another
+ * processor. When returning here, external interrupts
+ * are enabled.
+ */
+ cede_processor();
+
+ get_lppaca()->idle = 0;
}
}

@@ -453,15 +465,14 @@ static void __init pSeries_setup_arch(void)

pSeries_nvram_init();

- if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
+ if (firmware_has_feature(FW_FEATURE_LPAR)) {
vpa_init(boot_cpuid);
- ppc_md.power_save = pSeries_idle;
- }
-
- if (firmware_has_feature(FW_FEATURE_LPAR))
+ ppc_md.power_save = pseries_lpar_idle;
ppc_md.enable_pmcs = pseries_lpar_enable_pmcs;
- else
+ } else {
+ /* No special idle routine */
ppc_md.enable_pmcs = power4_enable_pmcs;
+ }

if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
long rc;
--
1.8.1.2


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