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Subject[RFC PATCH 22/35] subarch suport for idle loop (NO_IDLE_HZ for Xen)
Paravirtualize the idle loop to explicitly trap to the hypervisor when
blocking, and to use the NO_IDLE_HZ functionality introduced by s390
to inform the rcu subsystem that the CPU is quiescent.

Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
drivers/xen/Kconfig | 8 ++++++++
include/asm-i386/mach-xen/setup_arch_post.h | 24 ++++++++++++++++++++++++
2 files changed, 32 insertions(+)

--- xen-subarch-2.6.orig/drivers/xen/Kconfig
+++ xen-subarch-2.6/drivers/xen/Kconfig
@@ -12,6 +12,14 @@ config XEN

if XEN

+config NO_IDLE_HZ
+ bool
+ default y
+ help
+ Switches the regular HZ timer off when the system is going idle.
+ This helps Xen to detect that the Linux system is idle, reducing
+ the overhead of idle systems.
+
config XEN_SHADOW_MODE
bool
default y
--- xen-subarch-2.6.orig/include/asm-i386/mach-xen/setup_arch_post.h
+++ xen-subarch-2.6/include/asm-i386/mach-xen/setup_arch_post.h
@@ -8,6 +8,11 @@

#include <xen/interface/physdev.h>

+extern void stop_hz_timer(void);
+extern void start_hz_timer(void);
+
+void xen_idle(void);
+
static char * __init machine_specific_memory_setup(void)
{
unsigned long max_pfn = xen_start_info->nr_pages;
@@ -74,4 +79,23 @@ static void __init machine_specific_arch
console_use_vt = 0;
conswitchp = NULL;
}
+
+ pm_idle = xen_idle;
+}
+
+void xen_idle(void)
+{
+ local_irq_disable();
+
+ if (need_resched())
+ local_irq_enable();
+ else {
+ clear_thread_flag(TIF_POLLING_NRFLAG);
+ smp_mb__after_clear_bit();
+ stop_hz_timer();
+ /* Blocking includes an implicit local_irq_enable(). */
+ HYPERVISOR_sched_op(SCHEDOP_block, 0);
+ start_hz_timer();
+ set_thread_flag(TIF_POLLING_NRFLAG);
+ }
}
--
-
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