async: Asynchronous function calls to speed up kernel boot

Right now, most of the kernel boot is strictly synchronous, such that
various hardware delays are done sequentially.

In order to make the kernel boot faster, this patch introduces
infrastructure to allow doing some of the initialization steps
asynchronously, which will hide significant portions of the hardware delays
in practice.

In order to not change device order and other similar observables, this
patch does NOT do full parallel initialization.

Rather, it operates more in the way an out of order CPU does; the work may
be done out of order and asynchronous, but the observable effects
(instruction retiring for the CPU) are still done in the original sequence.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/kernel/irq/autoprobe.c b/kernel/irq/autoprobe.c
index cc0f7321b8ce..1de9700f416e 100644
--- a/kernel/irq/autoprobe.c
+++ b/kernel/irq/autoprobe.c
@@ -10,6 +10,7 @@
 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/delay.h>
+#include <linux/async.h>
 
 #include "internals.h"
 
@@ -34,6 +35,10 @@ unsigned long probe_irq_on(void)
         unsigned int status;
         int i;
 
+        /*
+         * quiesce the kernel, or at least the asynchronous portion
+         */
+        async_synchronize_full();
         mutex_lock(&probing_active);
         /*
          * something may have generated an irq long ago and we want to