[Xen-devel] [PATCH RFC v3 3/6] sched/idle: Add a generic poll before enter real idle path

[Quan Xu <quan.xu03@xxxxxxxxx>]

From: Yang Zhang <yang.zhang.wz@xxxxxxxxx>

Implement a generic idle poll which resembles the functionality
found in arch/. Provide weak arch_cpu_idle_poll function which
can be overridden by the architecture code if needed.

Interrupts arrive which may not cause a reschedule in idle loops.
In KVM guest, this costs several VM-exit/VM-entry cycles, VM-entry
for interrupts and VM-exit immediately. Also this becomes more
expensive than bare metal. Add a generic idle poll before enter
real idle path. When a reschedule event is pending, we can bypass
the real idle path.

Signed-off-by: Quan Xu <quan.xu0@xxxxxxxxx>
Signed-off-by: Yang Zhang <yang.zhang.wz@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Kyle Huey <me@xxxxxxxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Tobias Klauser <tklauser@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/process.c |    7 +++++++
 kernel/sched/idle.c       |    2 ++
 2 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c676853..f7db8b5 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -333,6 +333,13 @@ void arch_cpu_idle(void)
        x86_idle();
 }
 
+#ifdef CONFIG_PARAVIRT
+void arch_cpu_idle_poll(void)
+{
+       paravirt_idle_poll();
+}
+#endif
+
 /*
  * We use this if we don't have any better idle routine..
  */
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 257f4f0..df7c422 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
 }
 
 /* Weak implementations for optional arch specific functions */
+void __weak arch_cpu_idle_poll(void) { }
 void __weak arch_cpu_idle_prepare(void) { }
 void __weak arch_cpu_idle_enter(void) { }
 void __weak arch_cpu_idle_exit(void) { }
@@ -219,6 +220,7 @@ static void do_idle(void)
         */
 
        __current_set_polling();
+       arch_cpu_idle_poll();
        quiet_vmstat();
        tick_nohz_idle_enter();
 
-- 
1.7.1


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