PM / suspend: make sync() on suspend-to-RAM build-time optional

The Linux kernel suspend path has traditionally invoked sys_sync()
before freezing user threads.

But sys_sync() can be expensive, and some user-space OS's do not want
the kernel to pay the cost of sys_sync() on every suspend -- preferring
invoke sync() from user-space if/when they want it.

So make sys_sync on suspend build-time optional.

The default is unchanged.

Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 53266b729fd9..7e4cda4a8dd9 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -484,11 +484,13 @@ static int enter_state(suspend_state_t state)
         if (state == PM_SUSPEND_FREEZE)
                 freeze_begin();
 
+#ifndef CONFIG_SUSPEND_SKIP_SYNC
         trace_suspend_resume(TPS("sync_filesystems"), 0, true);
         printk(KERN_INFO "PM: Syncing filesystems ... ");
         sys_sync();
         printk("done.\n");
         trace_suspend_resume(TPS("sync_filesystems"), 0, false);
+#endif
 
         pr_debug("PM: Preparing system for sleep (%s)\n", pm_states[state]);
         error = suspend_prepare(state);