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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>
This commit is contained in:
Len Brown 2015-07-31 12:46:17 -04:00 committed by Rafael J. Wysocki
parent 019d8817b1
commit 2fd77fff4b
2 changed files with 12 additions and 0 deletions
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10
kernel/power/Kconfig
View File

@ -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

2
kernel/power/suspend.c
View File

@ -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);