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>

diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 9e30231..02e8dfa 100644 (file)
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -18,6 +18,16 @@ config SUSPEND_FREEZER
 
          Turning OFF this setting is NOT recommended! If in doubt, say Y.
 
+config SUSPEND_SKIP_SYNC
+       bool "Skip kernel's sys_sync() on suspend to RAM/standby"
+       depends on SUSPEND
+       depends on EXPERT
+       help
+         Skip the kernel sys_sync() before freezing user processes.
+         Some systems prefer not to pay this cost on every invocation
+         of suspend, or they are content with invoking sync() from
+         user-space before invoking suspend.  Say Y if that's your case.
+
 config HIBERNATE_CALLBACKS
        bool
 

diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 53266b7..7e4cda4 100644 (file)
--- 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);