PM / suspend: make sync() on suspend-to-RAM build-time optional (2fd77fff) · Commits · 戴 / test

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>

kernel/power/Kconfig

+10 −0

Original line number	Diff line number	Diff line
		@@ -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

kernel/power/suspend.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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);

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