On Sat, 4 Jul 2015, Rafael J. Wysocki wrote:

The only argument against dropping sys_sync() from the suspend code path
I've seen in this thread that I entirely agree with is that it may lead to
regressions, because we've done it practically forever and it may hide latent
bugs somewhere in block drivers etc.  Dropping it, though, is the only way
to see those bugs, if any, and if we want to ever fix them, we need to see
them.  That's why I think that it may be a good idea to allow people to
drop it if they are willing to accept some extra risk (via the kernel
command line, for example).

I'd be perfectly happy to have the sync selectable at runtime, one way 
or another.  The three most reasonable options seem to be:

	kernel command line

	sysfs file

	sysctl setting

The command line is less flexible (it can't be changed after booting).  
Either of the other two would be fine with me.

Moreover, question is if we really need to carry out the sync on *every*
suspend even if it is not pointless overall.  That shouldn't really be
necessary if we suspend and resume often enough or if we resume only for
a while and then suspend again.  Maybe it should be rate limited somehow
at least?

For example, skip the sync if the system has been awake for < 100 ms?  
The cutoff time could also be controlled by the sysfs file: -1 =>
never sync, 0 => always sync, > 0 => sync if the system has been awake 
longer than the value.

Alan Stern