On 03.10.14 at 23:40, <boris.ostrovsky@xxxxxxxxxx> wrote:
@@ -274,3 +292,176 @@ void vpmu_dump(struct vcpu *v)
vpmu->arch_vpmu_ops->arch_vpmu_dump(v);
}
+static atomic_t vpmu_sched_counter;
+
+static void vpmu_sched_checkin(unsigned long unused)
+{
+ atomic_inc(&vpmu_sched_counter);
+}
+
+static int vpmu_force_context_switch(void)
+{
+ unsigned i, numcpus, mycpu;
+ s_time_t start;
+ static DEFINE_PER_CPU(struct tasklet *, sync_task);
+ int ret = 0;
+
+ numcpus = num_online_cpus();
+ mycpu = smp_processor_id();
+
+ for ( i = 0; i < numcpus; i++ )
for_each_online_cpu() would have saved you from running into ...
+ {
+ if ( i == mycpu )
+ continue;
+
+ per_cpu(sync_task, i) = xmalloc(struct tasklet);
... a crash here when some CPU other than the highest numbered
one got offlined.
+ if ( per_cpu(sync_task, i) == NULL )
+ {
+ printk(XENLOG_WARNING "vpmu_force_context_switch: out of
memory\n");
+ ret = -ENOMEM;
+ goto out;
+ }
+ tasklet_init(per_cpu(sync_task, i), vpmu_sched_checkin, 0);
+ }
+
+ /* First count is for self */
+ atomic_set(&vpmu_sched_counter, 1);
+
+ for_each_online_cpu( i )
And oddly enough you use it here (albeit with malformed style -
either you drop the two blanks inside the parentheses or you add
another before the opening one)...
+ {
+ if ( i != mycpu )
+ tasklet_schedule_on_cpu(per_cpu(sync_task, i), i);
+ }
+
+ vpmu_save(current);
+
+ start = NOW();
+
+ /*
+ * Note that we may fail here if a CPU is hot-plugged while we are
+ * waiting. We will then time out.
+ */
+ while ( atomic_read(&vpmu_sched_counter) != numcpus )
+ {
+ s_time_t now;
+
+ cpu_relax();
+
+ now = NOW();
+
+ /* Give up after 5 seconds */
+ if ( now > start + SECONDS(5) )
+ {
+ printk(XENLOG_WARNING
+ "vpmu_force_context_switch: failed to sync\n");
+ ret = -EBUSY;
+ break;
+ }
+
+ /* Or after (arbitrarily chosen) 2ms if need to be preempted */
+ if ( (now > start + MILLISECS(2)) && hypercall_preempt_check() )
+ {
+ ret = -EAGAIN;
+ break;
+ }
+ }
So this time round you don't retain any state between retries at all.
How is this process expected to ever complete on a large and loaded
enough system?
