[Xen-changelog] Fix Xen idle loop to enter/exit tickless mode in same way as s390,

[BitKeeper Bot <riel@xxxxxxxxxxx>]

ChangeSet 1.1888, 2005/05/30 11:18:30+01:00, kaf24@xxxxxxxxxxxxxxxxxxxx

        Fix Xen idle loop to enter/exit tickless mode in same way as s390,
        which interfaces properly with the RCU subsystem.
        
        This includes a patch that fixes a race in the generic RCU code: it
        was created by IBM for s390, and is being pushed upstream by them.
        
        Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>



 linux-2.6.11-xen-sparse/arch/xen/i386/kernel/process.c |   17 +-----
 linux-2.6.11-xen-sparse/arch/xen/i386/kernel/time.c    |   43 +++++++----------
 patches/linux-2.6.11/rcu-nohz.patch                    |   11 ++++
 3 files changed, 35 insertions(+), 36 deletions(-)


diff -Nru a/linux-2.6.11-xen-sparse/arch/xen/i386/kernel/process.c 
b/linux-2.6.11-xen-sparse/arch/xen/i386/kernel/process.c
--- a/linux-2.6.11-xen-sparse/arch/xen/i386/kernel/process.c    2005-05-30 
07:04:38 -04:00
+++ b/linux-2.6.11-xen-sparse/arch/xen/i386/kernel/process.c    2005-05-30 
07:04:38 -04:00
@@ -91,25 +91,18 @@
 EXPORT_SYMBOL(enable_hlt);
 
 /* XXX XEN doesn't use default_idle(), poll_idle(). Use xen_idle() instead. */
-extern int set_timeout_timer(void);
+extern void stop_hz_timer(void);
+extern void start_hz_timer(void);
 void xen_idle(void)
 {
-       int cpu;
-
        local_irq_disable();
 
-       cpu = smp_processor_id();
-       if (rcu_pending(cpu))
-               rcu_check_callbacks(cpu, 0);
-
        if (need_resched()) {
                local_irq_enable();
-       } else if (set_timeout_timer() == 0) {
-               /* NB. Blocking reenable events in a race-free manner. */
-               HYPERVISOR_block();
        } else {
-               local_irq_enable();
-               HYPERVISOR_yield();
+               stop_hz_timer();
+               HYPERVISOR_block(); /* implicit local_irq_enable() */
+               start_hz_timer();
        }
 }
 
diff -Nru a/linux-2.6.11-xen-sparse/arch/xen/i386/kernel/time.c 
b/linux-2.6.11-xen-sparse/arch/xen/i386/kernel/time.c
--- a/linux-2.6.11-xen-sparse/arch/xen/i386/kernel/time.c       2005-05-30 
07:04:38 -04:00
+++ b/linux-2.6.11-xen-sparse/arch/xen/i386/kernel/time.c       2005-05-30 
07:04:38 -04:00
@@ -665,36 +665,31 @@
 }
 
 /*
- * This function works out when the the next timer function has to be
- * executed (by looking at the timer list) and sets the Xen one-shot
- * domain timer to the appropriate value. This is typically called in
- * cpu_idle() before the domain blocks.
- * 
- * The function returns a non-0 value on error conditions.
- * 
- * It must be called with interrupts disabled.
+ * stop_hz_timer / start_hz_timer - enter/exit 'tickless mode' on an idle cpu
+ * These functions are based on implementations from arch/s390/kernel/time.c
  */
-int set_timeout_timer(void)
+void stop_hz_timer(void)
 {
-       u64 alarm = 0;
-       int ret = 0;
+       unsigned int cpu = smp_processor_id();
        unsigned long j;
 
-       /*
-        * This is safe against long blocking (since calculations are
-        * not based on TSC deltas). It is also safe against warped
-        * system time since suspend-resume is cooperative and we
-        * would first get locked out. It is safe against normal
-        * updates of jiffies since interrupts are off.
-        */
-       j = next_timer_interrupt();
-       alarm = __jiffies_to_st(j);
+       /* s390 does this /before/ checking rcu_pending(). We copy them. */
+       cpu_set(cpu, nohz_cpu_mask);
 
-       /* Failure is pretty bad, but we'd best soldier on. */
-       if ( HYPERVISOR_set_timer_op(alarm) != 0 )
-               ret = -1;
+       /* Leave ourselves in 'tick mode' if rcu or softirq pending. */
+       if (rcu_pending(cpu) || local_softirq_pending()) {
+               cpu_clear(cpu, nohz_cpu_mask);
+               j = jiffies + 1;
+       } else {
+               j = next_timer_interrupt();
+       }
 
-       return ret;
+       BUG_ON(HYPERVISOR_set_timer_op(__jiffies_to_st(j)) != 0);
+}
+
+void start_hz_timer(void)
+{
+       cpu_clear(smp_processor_id(), nohz_cpu_mask);
 }
 
 void time_suspend(void)
diff -Nru a/patches/linux-2.6.11/rcu-nohz.patch 
b/patches/linux-2.6.11/rcu-nohz.patch
--- /dev/null   Wed Dec 31 16:00:00 196900
+++ b/patches/linux-2.6.11/rcu-nohz.patch       2005-05-30 07:04:38 -04:00
@@ -0,0 +1,16 @@
+diff -ur linux-2.6.11/kernel/rcupdate.c linux-2.6.11-rcu/kernel/rcupdate.c
+--- linux-2.6.11/kernel/rcupdate.c     2005-05-30 10:51:41 +01:00
++++ linux-2.6.11-rcu/kernel/rcupdate.c 2005-05-30 10:53:53 +01:00
+@@ -202,8 +202,11 @@
+  */
+ static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp, struct rcu_state *rsp)
+ {
++      cpumask_t mask;
++
+       cpu_clear(cpu, rsp->cpumask);
+-      if (cpus_empty(rsp->cpumask)) {
++      cpus_andnot(mask, rsp->cpumask, nohz_cpu_mask);
++      if (cpus_empty(mask)) {
+               /* batch completed ! */
+               rcp->completed = rcp->cur;
+               rcu_start_batch(rcp, rsp, 0);

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