From: Len Brown <len.br...@intel.com>
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.br...@intel.com>
---
kernel/power/Kconfig | 10 ++++++++++
kernel/power/suspend.c | 2 ++
2 files changed, 12 insertions(+)
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 7e01f78..80afa8a 100644
--- 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
+ Delete the kernel sys_sync() before freezing user processes.
+ Some operating 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.
+
config HIBERNATE_CALLBACKS
bool
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 8d7a1ef..4a942ee 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -482,11 +482,13 @@ 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 %s sleep\n", pm_states[state]);
error = suspend_prepare(state);
--
2.5.0
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