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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